+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

CCB Application Notes:

1. Character(s) preceded & followed by these symbols (

) or (

)

are super- or subscripted, respectively.

EXAMPLES: 42m

= 42 cubic meters

= carbon dioxide

2. All degree symbols have been replaced with the word deg.

3. All plus or minus symbols have been replaced with the symbol +/-.

4. All table note letters and numbers have been enclosed in square

brackets in both the table and below the table.

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.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

Naval Facilities Engineering Command
200 Stovall Street
Alexandria, Virginia 22332-2300 APPROVED FOR PUBLIC RELEASE

Foundations &
Earth Structures

DESIGN MANUAL 7.02
REVALIDATED BY CHANGE 1 SEPTEMBER 1986

NAVAL FACILITIES ENGINEERING COMMAND
PUBLICATIONS TRANSMITTAL

SN 0525-LP-300-7071

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1. TITLE NUMBER DATE

DM-7.02
FOUNDATIONS ANTD EARTH STRUCTURES Change 1 September 1986

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2. ATTACHMENTS

New Cover.
New Record of Document Changes page.
New pages iii through xiv.
New pages 7.2-35 through 7.2-38.
New pages 7.2-47 through 7.2-50.
New pages 7.2-53 and 7.2-54.
New pages 7.2-57 through 7.2-64.
New pages 7.2-127 through 7.2-130.
New pages 7.2-151 and 7.2-152.
New pages 7.2-175 through 7.2-178.
New pages 7.2-243 and 7.2-244.
New DD Form 1426.

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3. EXPLANATION

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dated September 1986.
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Insert new DD Form 1426 in back of manual.

DM-7.02 FOUNDATIONS AND EARTH STRUCTURES is revalidated for three years
after incorporation of this change.

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4. DISTRIBUTION

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SN 0525-LP-300-7071

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

1. TITLE NUMBER DATE

DM-7.02
FOUNDATIONS ANTD EARTH STRUCTURES Change 1 September 1986

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

2. ATTACHMENTS

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

3. EXPLANATION

Remove old cover dated May 1982 and replace with attached new cover
dated September 1986.
Insert new Record of Document Changes page immediately after new cover
page.
Remove paged 7.2-iii through 7.2-xvii and replace with attached new
pages iii through xiv.
Remove pages 7.2-35 through 7.2-38 and replace with attached new pages
7.2-35 through 7.2-38.
Remove pages 7.2-47 through 7.2-50 and replace with attached new pages
7.2-47 through 7.2-50.
Remove pages 7.2-53 and 7.2-54 and replace with attached new pages
7.2-53 and 7.2-54.
Remove pages 7.2-57 through 7.2-64 and replace with attached next
pages
7.2-57 through 7.2-64.
Remove pages 7.2-127 through 7.2-130 and replace with attached new
pages 7.2-127 through 7.2-130.
Remove pages 7.2-151 and 7.2-152 and replace with attached new pages
7.2-151 and 7.2-152.
Remove pages 7.2-175 through 7.2-173 and replace with attached new
pages 7.2-175 through 7.2-178.
Remove pages 7.2-243 and 7.2-244 and replace with attached new pages
7.2-243 and 7.2-244.
Insert new DD Form 1426 in back of manual.

DM-7.02 FOUNDATIONS AND EARTH STRUCTURES is revalidated for three
years after incorporation of this change.

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

4. DISTRIBUTION

See reverse.

NAVFAC DM/P MANUAL DISTRIBUTION (01/87):
(1 copy each unless otherwise specified)
SNDL
39B COMCB
49 ADMSUPPU
A2A NAVY STAFF (ONR only)
A3 CHIEF OF NAVAL OPERATIONS
A5 NAVPERS & BUMED
A6 COMMANDANT MC (code LFF)
B2A (JCS, NSA, DLA, DNA only)
B5 USCG only)
E3A LAB ONR(Wash.DC only)
FA6 NAVAIRSTA LANT
FA7 NAVSTA LANT
FAIO SUB BASE LANT
FA18 PHIBASE LANT
FA23 NAVFAC LANT
FA32 CINCLANT CBU
FB6 NAVAIRFAC PAC
FB7 NAVAIRSTA PAC
FB10 NAVSTA PAC (Seattle only)
FB13 SUBASE PAC (Bangor only)
FB21 PHIBASE PAC
FB34 FLEACTPAC (Kadena,Sasebo only)
FB36 FAC PAC
FB48 SUPPFAC PAC
FC3 ACTIVITY EUR (London only)
FC5 SUPPORT ACTIVITY EUR
FC7 NAVAL STATION EUR
FC12 FLEET SUPPORT OFFICE
FC14 NAVAIRSTA EUR
FDl OCEANOGRAPHY COMM
FE1 SECURITY GROUP HQ
FE2 SECURITY STATION
FE4 SECGRUACT (Edzell, Hanza
Homestead, Sabana Seca,
Sonoma, Winter Harbor only)
FF6 NAVAL OBSERVATORY
FF38 NAVAL ACADEMY
FG1 TELECOMMCOM
FG2 COMSTA (Balboa, Harold Holt,
Nea Makri, Thurso, Stockton,
Yokosuka, San miguel only)
FG3 COMM UNIT (East Machias only)
FG6 CA MASTER STAS (Norfolk only)
FH1 COMNAVMEDCOM
FKA1A SYSCOM, AIR
FKA1B SYSCOM, ELEX
FKA1C NAVFAC, (Code 04M2, 30 copies)
FKA1F SYSCOM, SUP
FKA1G SYSCOM, SEA
FKM8 SUPPLY ANNEX
FKM9 NSC (Oakland only)
FKM13 SHIPS PARTS & CONTROL CEN
FKM15 ASO (Philadelphia only)
FKN1 LANTDIV (100 copies)
CHESDIV ( 50 copies)
NORTHDIV (75 copies)
PACDIV, SOUIHDIV,
WESTDIV, (200 copies each)
FKN2 CBC

FKN3 OICC (6 copies each)
FKN5 PWC (5 copies each)
FKN7 ENERGY ENVIRON SUPP ACT
FKN10 SUPPORT ACT NAV FAC
FKN11 CIVIL ENGINEERING LAB
FKP1B WEAPONS STATION
FKP1E UNDERSEA WARFARE ENGR STA
FKP1J NAVAL ORDNANCE STATION
FKP1M WEAPONS SUPPLY CENTER
FKP7 NAVAL SHIPYARDS
FKQ3A ELECTRONIC STMS ENGR CEN
FKQ6A AIR DEVELOPMENT CENTER
FKQ6B COASTAL SYSTEMS CENTER
FKQ6C OCEAN SYSTEMS CENTER
FKQ6E SHIP RESEARCH & DEV.CEN,
FKQ6F SURFACE WEAPONS CENTER
FKQ6G UNDERWATER SYSTEMS CEN'TER
FKQ6H NAVAL WEAPONS CENTER
FKR1A AIR STATIONS R & D
FKR1B AIR REWORK FACILITY
FKR3A AIR ENGINEERING CENTER
FKR3H AIR PROPULSION CENTER
FKR4B MISSILE RANGE FACILITY
FKR5 AVIONICS CENTER
FKR7E AVIATION LOGISTICS CENTER
FR3 AIR STATIONS
FR4 AIR FACILITIES
FR15 SUPPACT
FT1 CHIEF NAVAL ENGR. TRAINING
FT2 CHIEF NAVAL AIR TRAINING
FT6 AIR STATIONS CNET
FT13 AIR TECH TRAINING CEN
FT10 CONSTR, BATTALION UNIT CBC
FT19 ADMINCOM (San Diego only)
FT22 FLECOMBATRACEN (Va. Beach only)
FT28 EDUCATION & TRAINING CEN
FT31 TRAINING CENTER
FT37 SCHOOL CEC OFFICERS
FT55 SCHOOL SUPPLY CORPS
FT78 ED & TRNG PGM DEV CEN
V2 MARCORPS BARRACKS SUPPORT
V3 MC AIR BASE COMMAND
V5 MCAS (less Beaufort)
V5 MCAS (Beaufort only,5 cys)
V8 MC RECRUIT DEPOT
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V15 MC DISTRICT
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REMAINDER TO: RECEIVING OFFICER
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RECORD OF DOCUMENT CHANGES

Instructions: DISCARD EXISTING SHEET AND INSERT THIS NEW RECORD OF DOCUMENT
CHANGES.

This is an inventory of all changes made to this design manual. Each change
is consecutively numbered, and each change page in the design manual
includes the date of the change which issued it.

Change Description Date of Page
Number of Change Change Change

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

1 Added new cover with revalidation date. September
1986 Cover

Added Record of Document Changes. -

New Abstract. iii

Added to Foreword instruction for sending
recommended changes to changed signature
to RADM Jones. v

Added listing of DM-7 series. vi

Deleted Preface. vii

Deleted list of Design Manuals. ix

New Table of Contents. vii-xiii

New Acknowledgments. xiv

Added NAVFAC P-418 to Reference list. 7.2-36

Updated Related Criteria listing. 7.2-37

Changed Note 1 to Table 4 to reflect
Modified Proctor test rather than
Standard Proctor. 7.2-47

Corrected spelling "moisture". 7.2-50

Corrected equation for Borrow Volume "V

7.2-53

Added NAVFAC DM's to Reference list. 7.2-57

Updated Related Criteria listing. 7.2-59

Added "Figure 3" to first note of Figure 2. 7.2-62

Deleted the -40 deg., +25 deg., and +30 deg.
lines from Figure 3. 7.2-64

RECORD OF DOCUMENT CHANGES (continued)

Change Description Date of Page
Number of Change Change Change

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

Added NAVFAC D14's to Reference list. 7.2-127

Changed DM-2 to EM-2.02 in paragraph
Related Criteria. 7.2-129

Changed "Figure 1" to "Figure 6" in first
step. 7.2-151

Added NAVFAC DM's to Reference list. 7.2-175

Updated Related Criteria listing. 7.2-177

Added NAVFAC DM's to Reference list. 7.2-244

Added DD Form 1426. -

ABSTRACT

This manual covers the application of basic engineering principles of
soil mechanics in the design of foundations and earth structures for naval
shore facilities. It is intended for use by experienced engineers. The
contents include: excavations; compaction, earthwork, and hydraulic fills;
analysis of walls and retaining structures; shallow foundations; and deep
foundations.

iii Change 1, September 1986

PAGE iv INTENTIONALLY BLANK

FOREWORD

This design manual is one of a series developed from an evaluation of
facilities in the shore establishment, from surveys of the availability of
new materials and construction methods, and from selection of the best
design practices of the Naval Facilities Engineering Command (NAFACENGCOM),
other Government agencies, and the private sector. This manual uses, to
the maximum extent feasible, national professional society, association, and
institute standards in accordance with NAVFACENGCOM policy. Deviations from
these criteria should not be made without prior approval of NAVFACENGCOM
Headquarters (Code 04).

Design cannot remain static any more than the naval functions it serves or
the technologies it uses. Accordingly, recommendations for improvement are
encouraged from within the Navy and from the private sector and should be
furnished to Commander, Naval Facilities Engineering command (Code 04B), 200
Stovall Street, Alexandria, VA 22332-2300.

This publication is certified as an official publication of the Naval
Facilities Engineering Command and has been reviewed and approved in
accordance with SECNNAVINST 5600.16, Procedures Governing Review of the
Department of the Navy (DN) Publications.

J. P. JONES, JR.
Rear Admiral, CEC, U. S. Navy
Commander
Naval Facilities Engineering Command

SOILS AND FOUNDATIONS DESIGN MANUALS

DM Number Title

)))))))))

)))))

7.01 Soil Mechanics

7.02 Foundations and Earth Structures

7.03 Soil Dynamics, Deep Stabilization,
and Special Geotechnical
Construction

Change 1, September 1986 vi

CONTENTS

Page

CHAPTER 1. EXCAVATIONS

Section 1. Introduction.......................................7.2-1
Section 2. Open Cuts..........................................7.2-1
Section 3. Trenching..........................................7.2-2
Section 4. Braced Excavations.................................7.2-13
Section 5. Rock Excavation....................................7.2-19
Section 6. Groundwater Control................................7.2-27
Section 7. Excavation Stabilization, Monitoring, and Safety...7.2-27

CHAPTER 2. COMPACTION, EARTHWORK, AND HYDRAULIC FILLS

Section 1. Introduction.......................................7.2-37
Section 2. Embankment Cross-Section Design....................7.2-38
Section 3. Compaction Requirements and Procedures.............7.2-45
Section 4. Embankment Compaction Control......................7.2-50
Section 5. Borrow Excavation..................................7.2-52
Section 6. Hydraulic and Underwater Fills.....................7.2-54

CHAPTER 3. ANALYSIS OF WALLS AND RETAINING STRUCTURES

Section 1. Introduction.......................................7.2-59
Section 2. Computation of Wall Pressures......................7.2-59
Section 3. Rigid Retaining Walls..............................7.2-82
Section 4. Design of Flexible Walls...........................7.2-85
Section 5. Cofferdams.........................................7.2-116

CHAPTER 4. SHALLOW FOUNDATIONS

Section 1. Introduction.......................................7.2-129
Section 2. Bearing Capacity...................................7.2-129
Section 3. Spread Footing Design Considerations...............7.2-146
Section 4. Mat and Continuous Beam Foundations................7.2-150
Section 5. Foundations on Engineered Fill.....................7.2-159
Section 6. Foundations on Expansive Soils.....................7.2-159
Section 7. Foundation Waterproofing...........................7.2-163
Section 8. Uplift Resistance..................................7.2-169

vii Change, September 1986

CHAPTER 5. DEEP FOUNDATIONS

Section 1. Introduction .....................................7.2-177
Section 2. Foundation Types and Design Criteria..............7.2-178
Section 3. Bearing Capacity and Settlement...................7.2-191
Section 4. Pile Installation and Load Tests..................7.2-213
Section 5. Distribution of Loads on Pile Groups..............7.2-230
Section 6. Deep Foundations on Rock..........................7.2-232
Section 7. Lateral Load Capacity.............................7.2-234

BIBLIOGRAPHY

.....................................................7.2-B-1

APPENDIX A - Listing of Computer Programs

GLOSSARY

.........................................................7.2-G-1

SYMBOLS

..........................................................7.2-S-1

INDEX

............................................................7.2-INDEX-1

Change, September 1986 viii

FIGURES

Figure Title Page

CHAPTER 1

1 Sliding Trench Shield...........................................7.2-7
2 Skeleton Shoring................................................7.2-10
3 Close (Tight) Sheeting..........................................7.2-11
4 Box Shoring................................................... 7.2-12
5 Telescopic Shoring..............................................7.2-12
6 Support System - Walled Excavation..............................7.2-15
7 General Guidance for Underpinning...............................7.2-20
8 Rippability of Subsurface Materials Related to Longitudinal
Seismic Velocity for a Heavy Duty Ripper (Tractor-Mounted)....7.2-22
9 Suggested Guide for Ease of Excavation..........................7.2-23
10 Cube Root Scaling Versus Maximum Particle Velocity..............7.2-24
11 Guideline for Assessing Potential for Damage Induced by
Blasting Vibration to Residential Structure Founded on
Dense Soil or Rock............................................7.2-25
12 Guide for Predicting Human Response to Vibrations and
Blasting Effects..............................................7.2-26
13 Methods of Construction Dewatering..............................7.2-31
14 Limits of Dewatering Methods Applicable to Different Soils......7.2-33

CHAPTER 2

1 Resistance of Earth Dam Embankment Materials to Piping and
Cracking......................................................7.2-42

CHAPTER 3

1 Effect of Wall Movement on Wall Pressures.......................7.2-60
2 Computation of Simple Active and Passive Pressures..............7.2-62
3 Active and Passive Coefficients, Sloping Backfill
(Granular Soils)..............................................7.2-64
4 Position of Failure Surface for Active and Passive Wedges
(Granular Soils)..............................................7.2-65
5 Active and Passive Coefficients with Wall Friction
(Sloping Wall)................................................7.2-66
6 Active and Passive Coefficients with Wall Friction
(Sloping Backfill)............................................7.2-67
7 Computation of General Active Pressures.........................7.2-68
8 Coefficients K

A and K

for Walls with Sloping Wall and

Friction, and Sloping Backfill................................7.2-69
9 Computation of General Passive Pressures........................7.2-71
10 Effect of Groundwater Conditions on Wall Pressures..............7.2-72
11 Horizontal Pressures on Rigid Wall from surface Load............7.2-74
12 Lateral Pressure on an Unyielding Wall Due to Uniform
Rectangular Surface Load......................................7.2-75

ix Change, September 1986

Figure Title Page

CHAPTER 3 (continued)

13 Horizontal Pressure on Walls from Compaction Effort.............7.2-77
14a Values of F for Determination of Dynamic Lateral Pressure
Coefficients..................................................7.2-79
14b Example Calculations for Dynamic Loading on Walls...............7.2-80
15 Design Criteria for Rigid Retaining Walls.......................7.2-83
16 Design Loads for Low Retaining Walls (Straight Slope Backfill)..7.2-86
17 Design Loads for Low Retaining Walls (Broken Slope Backfill)....7.2-87
18 Design Criteria for Anchored Bulkhead (Free Earth Support)......7.2-88
19 Reduction in Bending Moments in Anchored Bulkhead from Wall
Flexibility...................................................7.2-89
20 Design Criteria for Deadman Anchorage...........................7.2-91
21 Example of Analysis of Anchored Bulkhead........................7.2-93
22 Sand Dike Scheme for Controlling Active Pressure................7.2-94
23 Analysis for Cantilever Wall....................................7.2-95
24 Cantilever Steel Sheet Pile Wall in Homogeneous Granular Soil...7.2-97
25 Cantilever Steel Sheet Pile Wall in Cohesive Soil with
Granular Backfill.............................................7.2-98
26 Pressure Distribution for Brace Loads in Internally Braced
Flexible Walls................................................7.2-100
27 Design Criteria for Braced Flexible Walls.......................7.2-102
28 Stability of Base for Braced Cut................................7.2-104
29 Pressure Distribution for Tied-Back Walls.......................7.2-105
30 Example of Analysis of Pressures on Flexible Wall of Narrow
Cut in Clay - Undrained Conditions............................7.2-107
31 Example of Excavation in Stages.................................7.2-108
32 Culmann Method for Determining Passive Resistance of Earth
Berm (Granular Soil)..........................................7.2-113
33 Passive Pressure Distribution for Soldier Piles.................7.2-114
34 Gabion Wall.....................................................7.2-115
35 Reinforced Earth................................................7.2-117
36 Design Criteria for Crib and Bin Walls..........................7.2-118
37 Design Criteria for Cellular Cofferdams.........................7.2-119

CHAPTER 4

1 Ultimate Bearing Capacity of Shallow Footings with Concentric
Loads.........................................................7.2-131
2 Ultimate Bearing Capacity with Groundwater Effect...............7.2-132
3a Ultimate Bearing Capacity of Continuous Footings with Inclined
Load..........................................................7.2-133
3b Eccentrically Loaded Footings...................................7.2-134
4a Ultimate Bearing Capacity for Shallow Footing Placed on or
Near a Slope..................................................7.2-135
4b Bearing Capacity Factors for Shallow Footing Placed on or
Near a Slope..................................................7.2-136
5 Ultimate Bearing Capacity of Two Layer Cohesive Soil([theta]=0).7.2-137
6 Examples of Computation of Allowable Bearing Capacity Shallow
Footings on Cohesive Soils....................................7.2-139

Change 1, September 1986 x

Figure Title Page

CHAPTER 4 (continued)

7 Examples of Computation of Allowable Bearing Capacity Shallow
Footings on Granular Soils....................................7.2-140
8 Allowable Bearing Pressure for Sand from Static Cone
Penetration Tests.............................................7.2-147
9 Example of Proportioning Footing Size to Equalize Settlements...7.2-148
10 Computation of Shear, Moment, and Deflection, Berms on
Elastic Foundation............................................7.2-153
11 Functions for Shear, Moment, and Deflection, Beams on Elastic
Foundations...................................................7.2-154
12 Functions for Shear, Moment, and Deflections, Mats on Elastic
Foundations...................................................7.2-157
13 Limits of Compaction Beneath Square and Continuous Footings.....7.2-160
14 Construction Details for Swelling Soils.........................7.2-162
15 Typical Foundation Drainage and Waterproofing...................7.2-167
16 Capacity of Anchor Rods in Fractured Rock.......................7.2-170
17 Resistance of Footings and Anchorages to Combined Transient
Loads.........................................................7.2-171
18 Tower Guy Anchorage in Soil by Concrete Deadman.................7.2-172

CHAPTER 5

1 Load Carrying Capacity of Single Pile in Granular Soils.........7.2-193
2 Ultimate Load Capacity of Single Pile or Pier in Cohesive
Soils.........................................................7.2-196
3 Bearing Capacity of Pile Groups in Cohesive Soils...............7.2-206
4 Settlement of Pile Groups.......................................7.2-210
5 Principles of Operation of Pile Drivers.........................7.2-222
6 Interpretation of Pile Load Test................................7.2-229
7 Load Test Analysis Where Downdrag Acts on Piles.................7.2-231
8 Example Problem - Batter Pile Group as Guy Anchorage............7.2-233
9 Coefficient of Variation of Subgrade Reaction...................7.2-236
10 Design Procedure for Laterally Loaded Piles.....................7.2-237
11 Influence Values for Pile with Applied Lateral Load and
Moment (Case I. Flexible Cap or Hinged End Condition).........7.2-238
12 Influence Values for Laterally Loaded Pile (Case II. Fixed
Against Rotation at Ground Surface)...........................7.2-239
13 Slope Coefficient for Pile with Lateral Load or Moment..........7.2-240

xi Change, September 1986

TABLES

Table Title Page

CHAPTER 1

1 Factors Controlling Stability of sloped Cut in Some
Problem Soils.................................................7.2-3
2 Factors Controlling Excavation Stability........................7.2-4
3 OSHA Requirements (Minimum) for Trench Shoring..................7.2-8
4 Types of Walls..................................................7.2-14
5 Factors Involved in Choice of a Support System For a Deep
Excavation (> 20 feet)........................................7.2-16
6 Design Considerations for Braced and Tieback Walls..............7.2-17
7 Methods of Groundwater Control..................................7.2-28

CHAPTER 2

1 Typical Properties of Compacted Soils...........................7.2-39
2 Relative Desirability of Soils as Compacted Fill................7.2-40
3 Clay Dispersion Potential.......................................7.2-44
4 Compaction Requirements.........................................7.2-46
5 Compaction Equipment and Methods................................7.2-48
6 Methods of Fill Placement Underwater............................7.2-55

CHAPTER 3

1 Friction Factors and Adhesion for Dissimilar Materials..........7.2-63

CHAPTER 4

1 Presumptive Values of Allowable Bearing Pressure for Spread
Foundations...................................................7.2-142
2 Selection of Allowable Bearing Pressures for Spread
Foundations...................................................7.2-144
3 Definitions and Procedures, Analysis of Beams on Elastic
Foundation....................................................7.2-151
4 Definitions and Procedures, Mats on Elastic Foundations.........7.2-155
5 Requirements for Foundation Waterproofing and Dampproofing......7.2-164

CHAPTER 5

1 Design Criteria for Bearing Piles...............................7.2-179
2 Characteristics of Common Excavated/Drilled Foundations.........7.2-184
3 Design Parameters for side Friction for Drilled Piers in
Cohesive Soils................................................7.2-198
4 Application of Pile Driving Resistance Formulas.................7.2-203

Change 1, September 1986 xii

Table Title Page

CHAPTER 5 (continued)

5 Typical Values of Coefficient C

for Estimating Settlement

of a Single Pile..............................................7.2-208
6 General Criteria for Installation of Pile Foundations...........7.2-214
7 Supplementary Procedures and Appurtenances Used in Pile
Driving......................................................7.2-218
8 Impact and Vibratory Pile-Driver Data...........................7.2-219
9 Treatment of Field Problems Encountered During Pile Driving.....7.2-226
10 Drilled Piers: Construction Problems............................7.2-227

xiii Change 1, September 1986

ACKNOWLEDGEMENTS

Figure Acknowledgment

Figure 13, Mazurkiewicz, D.K., Design and Construction of Dry Docks,
Chapter 1 Trans Tech Publications, Rockport, MA., 1980.

Figure 1, Sherard, J.L., Influence of Soil Properties and
Chapter 2 Construction Methods on the Performance of Homogeneous
Earth Dams, Technical Memorandum 645, U.S. Department of
the Interior, Bureau of Reclamation.

Figures 5, 6 & Caquot, A., and Kerisel, J., Tables for the Calculation
7, Chapter 3 of Passive Pressure, Active Pressure and Bearing Capacity
of Foundations, Gauthier-Villars, Paris.

Figure 16 & 17 Terzaghi, K. and Peck, R.B., Soil Mechanics in
Chapter 3 Engineering Practice, John Wiley & Sons, Inc., New York,
NY.

Figures 23, 24 U.S. Steel, Sheet Piling Design Manual, July, 1975.
& 25, Chapter 3

Figure 36, Portland Cement Association, Concrete Crib Retaining
Chapter 3 Walls, Concrete Information No. St. 46, Chicago, IL.,
May, 1952.

Figures 10 & Hetenyi, M., Beams on Elastic Foundation, The University
11, Chapter 4 of Michigan Press, Ann Arbor, MI.

Figure 14, Parcher, J.V., and Means, R.E., Soil Mechanics and
Chapter 4 Foundations, Charles E. Merril Publishing Company,
Columbus, OH., 1968.

Figure 2,
Chapter 5 Skempton, A.W., The Bearing Capacity of Clays,
(upper panel, Proceedings, Building Research Congress, London, 1951.
right)

Change 1, September 1986 xiv

CHAPTER 1. EXCAVATIONS

Section 1. INTRODUCTION

1. SCOPE. This chapter covers the methods of evaluating the stability of
shallow and deep excavations. There are two basic types of excavations: (a)
"open excavations" where stability is achieved by providing stable side
slopes, and (b) "braced excavations" where vertical or sloped sides are
maintained with protective structural systems that can be restrained
laterally by internal or external structural elements. Guidance on
performance monitoring is given in DM-7.1, Chapter 2.

2. METHODOLOGY. In selecting and designing the excavation system, the
primary controlling factors will include: (a) soil type and soil strength
parameters; (b) groundwater conditions; (c) slope protection; (d) side and
bottom stability; and (e) vertical and lateral movements of adjacent areas,
and effects on existing structures.

3. RELATED CRITERIA. For additional criteria on excavations, see the
following source:

Subject Source

Dewatering and Groundwater Control of Deep Excavations....NAVFAC P-418

Section 2. OPEN CUTS

1. SLOPED CUTS.

a. General. The depth and slope of an excavation, and groundwater
conditions control the overall stability and movements of open excavations.
In granular soils, instability usually does not extend significantly below
the excavation provided seepage forces are controlled. In rock, stability
is controlled by depths and slopes of excavation, particular joint patterns,
in situ stresses, and groundwater conditions. In cohesive soils,
instability typically involves side slopes but may also include materials
well below the base of the excavation. Instability below the base of
excavation, often referred to as bottom heave, is affected by soil type and
strength, depth of cut, side slope and/or berm geometry, groundwater
conditions, and construction procedures. Methods for controlling bottom
heave are given in DM-7.1, Chapter 6.

b. Evaluation. Methods described in DM-7.1, Chapter 7 may be used to
evaluate the stability of open excavations in soils where behavior of such
soils can be reasonably determined by field investigation, laboratory
testing, and analysis. In certain geologic formations (stiff clays, shales,
sensitive clays, clay tills, etc.) stability is controlled by construction
procedures, side effects during and after excavation, and inherent geologic
planes of weaknesses- Table 1 (modified from Reference 1, Effects of
construction on Geotechnical Engineering, by Clough and Davidson) presents a

7.2-1

summary of the primary factors controlling excavation slopes in some problem
soils. Table 2 (modified from Reference 1 and Reference 2, Soils and
Geology, Procedures for Foundation Design of Buildings and Other Structures,
Departments of Army and Air Force) summarizes measures that can be used for
excavation protection for both conventional and problem soils.

2. VERTICAL CUTS. Many cuts in clays will stand with vertical slopes for a
period of time before failure occurs. However, changes in the shear
strength of the clay with time and stress release resulting from the
excavation can lead to progressive deterioration in stability. This process
can be rapid in stiff, highly fissured clays, but relatively slow in softer
clays. (See DM-7.1, Chapter 7 for critical heights for vertical cuts in
cohesive soils.) For cuts in hard unweathered rock, stability is mostly
controlled by strength along bedding planes, groundwater condition, and
other factors (see DM-7.1, Chapter 6 and Reference 3, Stability of Steep
Slopes on Hard Unweathered Rock, by Terzaghi for detailed discussion on the
effects of rock discontinuities). Cuts in rock can stand vertical without
bolting or anchoring depending on rock quality and joint pattern.

Section 3. TRENCHING

1. SITE EXPLORATION. Individual trenching projects frequently extend over
long distances. An exploration program should be performed to define the
soil and groundwater conditions over the full extent of the project, so that
the design of the shoring system can be adjusted to satisfy the varying site
conditions.

2. TRENCH STABILITY. Principal factors influencing trench stability are
the lateral earth pressures on the wall support system, bottom heave, and
the pressure and erosive effects of infiltrating groundwater (see Chapter 3
and DM-7.1, Chapter 6). External factors which influence trench stability
include:

a. Surface Surcharge. The application of any additional load between
the edge of the excavation and the intersection of the ground surface with
the possible failure plane must be considered in the stability analyses for
the excavation.

b. Vibration Loads. The effects of vibrating machinery, blasting or
other dynamic loads in the vicinity of the excavation must be considered.
The effects of vibrations are cumulative over periods of time and can be
particularly dangerous in brittle materials such as clayey sand or gravel.

c. Ground Water Seepage. Improperly dewatered trenches in granular
soils can result in quick conditions and a complete loss of soil strength or
bottom heave. (See DM-7.1, Chapter 6.)

d. Surface Water Flow. This can result in increased loads on the wall
support system and reduction of the shear strength of the soil. Site
drainage should be designed to divert water away from trenches.

7.2-2

TABLE 1
Factors Controlling Stability of Sloped Cut in Some Problem Soils

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

SOIL TYPE PRIMARY CONSIDERATIONS FOR SLOPE DESIGN

*)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Stiff-fissured Clays

Field shear resistance may be less than suggested by

and Shales

laboratory tests. Slope failures may occur progressively

and shear strengths reduced to residual values

compatible with relatively large deformations. Some

case histories suggest that the long-term performance

is controlled by the residual friction angle which for

some shales may be as low as 12 deg. The most reliable

design procedure would involve the use of local

experience and recorded observations.

*)))))))))))))))))))))*)))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Loess and Other

Strong potential for collapse and erosion of relatively

Collapsible Soils

dry material upon wetting. Slopes in loess are

frequently more stable when cut vertical to prevent

infiltration. Benches at intervals can be used to

reduce effective slope angles. Evaluate potential for

collapse as described in DM 7.1, Chapter 1. (See

DM-7.3, Chapter 3 for further guidance.)

*)))))))))))))))))))))*)))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Residual Soils

Significant local variations in properties can be

expected depending on the weathering profile from

parent rock. Guidance based on recorded observation

provides prudent basis for design.

*)))))))))))))))))))))*)))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Sensitive Clays

Considerable loss of strength upon remolding generated

by natural or man-made disturbance. Use analyses

based on unconsolidated undrained tests or field vane

tests.

*)))))))))))))))))))))*)))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Talus

Talus is characterized by loose aggregation of rock

that accumulates at the foot of rock cliffs. Stable

slopes are commonly between 1-1/4 to 1-3/4 horizontal

to 1 vertical. Instability is associated with abundance

of water, mostly when snow is melting.

*)))))))))))))))))))))*)))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Loose Sands

May settle under blasting vibration, or liquify,

settle, and lose strength if saturated. Also prone to

erosion and piping.

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-3

3. SUPPORT SYSTEMS. Excavation support systems commonly used are as
follows:

a. Trench Shield. A rigid prefabricated steel unit used in lieu of
shoring, which extends from the bottom of the excavation to within a few
feet of the top of the cut. Pipes are laid within the shield, which is
pulled ahead, as trenching proceeds, as illustrated in Figure 1 (from
Reference 4, Cave-In! by Petersen). Typically, this system is useful in
loose granular or soft cohesive soils where excavation depth does not exceed
12 feet. Special shields have been used to depths of 30 feet.

b. Trench Timber Shoring. Table 3 illustrates the Occupational Safety
and Health Act's minimum requirements for trench shoring. Braces and
shoring of trench are carried along with the excavation. Braces and
diagonal shores of timber should not be subjected to compressive stresses in
excess of:

S = 1300 - 20 L/D

where: L = unsupported length (inches)

D = least side of the timber (inches)

S = allowable compressive stress in pounds per square
inch of cross section

Maximum Ratio L/D = 50

(1) Skeleton Shoring. Used in soils where cave-ins are expected.
Applicable to most soils to depth up to 20 feet. See Figure 2 (from
Reference 4) for illustration and guidance for skeleton shoring. Structural
components should be designed to safely withstand earth pressures.

(2) Close (Tight) Sheeting. Used in granular or other running
soils, compared to skeleton shoring, it is applicable to greater depths.
See illustration in Figure 3 (from Reference 4).

(3) Box Shoring. Applicable to trenching in any soil. Depth
limited by structural strength and size of timber. Usually limited to 40
feet. See illustration in Figure 4 (from Reference 4).

(4) Telescopic Shoring. Used for excessively deep trenches. See
illustration in Figure 5 (Reference 4).

c. Steel Sheeting and Bracing. Steel sheeting and bracing can be used
in lieu of timber shoring. Structural members should safely withstand water
and lateral earth pressures. Steel sheeting with timber wales and struts
have also been used.

7.2-6

7.2-10

7.2-11

Section 4. BRACED EXCAVATIONS

1. WALL TYPES. Commonly used wall types and limitations to be considered
in selection are given in Table 4. Schematics of support systems are shown
on Figure 6. A description of wall types listed in Table 4 is presented in
Reference 5, Lateral Support Systems and Underpinning, by Goldberg, et al.

2. SELECTION OF SUPPORT SYSTEM. Factors to be considered in selecting
types of support systems are given in Table 5.

3. EARTH PRESSURES. The two limiting pressures which may act on the wall
are the states of active pressure and passive pressure. Definitions and
methods for computing earth pressures are presented in Chapter 3.

For most practical cases, criteria for earth pressures do not exactly
conform to the state of active, passive or at rest pressure. Actual earth
pressure depends on wall deformation and this in turn depends on several
factors. Among the principal factors are: (1) stiffness of wall and support
systems; (2) stability of the excavation; and (3) depth of excavation and
wall deflection.

The effects of wall deflection on pressure distribution, and differences
between strut loads computed from active earth pressure theory and those
actually measured for deep excavation in soft clay, are illustrated in
Reference 6, Stability of Flexible Structures by Bjerrum, et al. As many
different variables affect pressures acting on walls, many types of analyses
are available for special situations. (Details concerning these are given
in Reference 7, Braced Excavation by Lambe.) Examples of earth pressure
computations are given in Chapter 3.

4. OTHER DESIGN AND CONSTRUCTION CONSIDERATIONS. Several factors other than
earth pressures affect the selection, design and the performance of braced
excavations. See Table 6 for a summary of these factors.

5. LATERAL MOVEMENTS. For well constructed strutted excavations in dense
sands and till, maximum lateral wall movements are often less than 0.2% of
excavation depth. Lateral movements are usually less for tied back walls.
In stiff fissured clays, lateral movements may reach 0.5% or higher
depending on quality of construction. In soft clays, a major portion of
movement occurs below excavation bottom. Lateral movement may be in the
range of 0.5% to 2% of excavation depth, depending on the factor of safety
against bottom instability. Higher movements are associated with lesser
factors of safety.

6. SOIL SETTLEMENTS BEHIND WALLS. Reference 8, Deep Excavations and
Tunneling in Soft Ground by Peck, provides guidance based on empirical
observation of settlement behind wall. Settlements up to about 1% of the
excavation depth have been measured behind well constructed walls for cuts
in sand and in medium stiff clays. In softer clays, this may be as high as
2% and considerably more in very soft clays.

7.2-13

TABLE 4
Types of Walls

+))))))))))))))))))))))))0)))))))))))))))))0))))))))))))))))))))))))))))))))),
*

Typical EI

Name

Values

Comments

Per Foot (ksf)

*))))))))))))))))))))))))3)))))))))))))))))/)))))))))))))))))))))))))))))))))1
*

(1) Steel Sheeting

900 -

- Can be impervious

90,000

- Easy to handle and construct

*))))))))))))))))))))))))3)))))))))))))))))/)))))))))))))))))))))))))))))))))1
*

(2) Soldier Pile and

2,000 -

- Easy to handle and construct

Lagging

120,000

- Permits drainage

- Can be driven or augered

*))))))))))))))))))))))))3)))))))))))))))))/)))))))))))))))))))))))))))))))))1
*

(3) Cast-in-place

288,000 -

- Can be impervious

or Pre-cast Con-

2,300,000

- Relatively high stiffness

crete Slurry

- Can be part of permanent

Wall (diaphragm

structure

walls, see DM-

- Can be prestressed

7.3, Chapter 3)

- Relatively less lateral wall

movement permitted compared

to (1) and (2)

- High initial cost

- Specialty contractor

required to construct

- Very large and heavy wall

must be used for deep

systems

- Permits yielding of sub-soils,

but precast concrete

usually shows less yielding

than steel sheeting or

soldier pile procedures.

*))))))))))))))))))))))))3)))))))))))))))))/)))))))))))))))))))))))))))))))))1
*

(4) Cylinder Pile

115,000 -

- Secant piles impervious

Wall

1,000,000

- Relatively high stiffness

- Highly specialized equipment

not needed for tangent piles

- Slurry not needed

.))))))))))))))))))))))))2)))))))))))))))))2)))))))))))))))))))))))))))))))))-

7.2-14

7.2-15

TABLE 5
Factors Involved in Choice of A Support System
For A Deep Excavation (> 20 feet)

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

Requirements

Lends Itself to Use Of

Comments

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

1. Open excavation

Tiebacks or rakers or

area

cantilever walls (shallow

excavation)

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

2. Low initial cost

Soldier pile or sheetpile

walls; combined soil slope

with wall

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

3. Use as part of

Diaphragm (see DM 7.3

Diaphragm wall most

permanent

Chapter 3) or cylinder

common as permanent

structure

pile walls

wall.

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

4. Deep, soft clay

Strutted or raker

Tieback capacity not

subsurface con-

supported diaphragm or

adequate in soft clays.

ditions

cylinder pile walls

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

5. Dense, gravelly

Soldier pile, diaphragm

Sheetpiles may lose

sand or clay

or cylinder pile

interlock on hard

subsoils

driving.

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

6. Deep, overcon-

Struts, long tiebacks or

High in situ lateral

solidated clays

combination tiebacks and

stresses are relieved

struts.

in overconsolidated

soils. Lateral

movements may be large

and extend deep into

soil.

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

7. Avoid dewatering

Diaphragm walls, possibly

Soldier pile wall is

sheetpile walls in soft

pervious.

subsoils

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

8. Minimize

High preloads on stiff

Analyze for stability

movements

strutted or tied-back wall

of bottom of

excavation.

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

9. Wide excavation

Tiebacks or rakers

Tiebacks preferable

(greater than

except in very soft

65 feet wide)

clay subsoils.

*)))))))))))))))))))))*))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))*

10. Narrow excava-

Crosslot struts

Struts more economical

tion (less than

but tiebacks still may

65 feet wide)

be preferred to keep

excavation open.

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-16

7. PROTECTION OF ADJACENT STRUCTURES. Evaluate the effects of braced
excavations on adjacent structures to determine whether existing building
foundations are to be protected. See DM-7.3, Chapters 2 and 3 on
stabilizing foundation soils and methods of underpinning. Figure 7
(modified from Reference 9, Damage to Brick Bearing Wall Structures Caused
by Adjacent Braced Cuts and Tunnels, by O'Rourke, et al.) illustrates areas
behind a braced wall where underpinning is or may be required.

Factors influencing the type of bracing used and the need for underpinning
include:

(a) Lateral distance of existing structure from the braced
excavation. Empirical observations on this can be found in Reference 8.

(b) Lowering groundwater can cause soil consolidation and settlement of
structures.

(d) Tolerance of structures to movement. See DM-7.1, Chapter 5 for
evaluation of tolerance of structure to vertical movements. Vertical and
lateral movements produce horizontal strains in structure. Guidance on
permissible horizontal strains for structures is given in Reference 9.

Section 5. ROCK EXCAVATION

1. OBJECTIVE. Primary objective is to conduct work in such a manner that a
stable excavation will be maintained and that rock outside the excavation
prism will not be adversely disturbed.

2. PRELIMINARY CONSIDERATIONS. Rock excavation planning must be based on
detailed geological data at the site. To the extent possible, structures to
be constructed in rock should be oriented favorably with the geological
setting. For example, tunnels should be aligned with axis perpendicular to
the strike of faults or major fractures. Downslope dip of discontinuities
into an open cut should be avoided.

In general, factors that must be considered in planning, designing and
constructing a rock excavation are as follows: (1) presence of strike, dip
of faults, folds, fractures, and other discontinuities; (2) in situ
stresses; (3) groundwater conditions; (4) nature of material filling joints
(5) depth and slope of cut; (6) stresses and direction of potential
sliding;surfaces; (7) dynamic loading, if any; (8) design life of cut as
compared to weathering or deterioration rate of rock face (9) rippability
and/or the need for blasting; and (10) effect of excavation and/or blasting
on adjacent structures.

The influence of most of these factors on excavations in rock is similar to
that of excavations in soil, see DM-7.1, Chapter 7.

7.2-19

7.2-20

3. RIPPABILITY. Excavation ease or rippability can be assessed
approximately from field observation in similar materials or by using
seismic velocity, fracture spacing, or point load strength index. Figure 8
(from Reference 10, Handbook of Ripping, by Caterpillar Tractor Co.) shows
an example of charts for heavy duty ripper performance (ripper mounted on
tracked bulldozer) as related to seismic wave velocity. Charts similar to
Figure 8 are available from various equipment manufacturers. Figure 8 is
for guidance and restricted in applicability to large tractors heavier than
50 tons with engine horsepower greater than 350 Hp. Ripper performance is
also related to configuration of ripper teeth, equipment condition and size,
and fracture orientation.

Another technique of relating physical properties of rock to excavation ease
is shown on Figure 9 (from Reference 11, Logging the Mechanical Character of
Rock, by Franklin, et al.) where fracture frequency (or spacing) is plotted
against the point load strength index corrected to a reference diameter of
50 mm. (See Reference 12, The Point-Load Strength Test, by Broch and
Franklin.)

A third and useful technique is exploration trenching in which the depth of
unrippable rock can be established by digging test trenches in rock using
rippers (or other excavation equipment) anticipated to be used for the
project. The size and shape of the area to be excavated is a significant
factor in determining the need for blasting, or the equipment needed to
remove the rock.

4. BLASTING. Of major concern is the influence of the blasting on adjacent
structures. The maximum particle velocity (the longitudinal velocity of a
particle in the direction of the wave that is generated by the blast) is
accepted as a criterion for evaluating the potential for structural damage
induced by blasting vibration. The critical level of the particle velocity
depends on the frequency characteristics of the structure, frequency of
ground and rock motion, nature of the overburden, and capability of the
structure to withstand dynamic stress. Figure 10 can be used for estimating
the maximum particle velocity, which can then be used in Figure 11 (from
Reference 13, Blasting Vibrations and Their Effects on Structures, by Bureau
of Mines) to estimate potential damage to residential structures. Guidance
for human response to blasting vibrations is given in Figure 12 (from
Reference 14, Engineering of Rock Blasting on Civil Protects, by Hendron).

Once it has been determined that blasting is required, a pre-blasting survey
should be performed. As a minimum, this should include: (a) examination of
the site; (b) detailed examination and perhaps photographic records of
adjacent structures; and (c) establishment of horizontal and vertical survey
control points. In addition, the possibility of vibration monitoring should
be considered, and monitoring stations and schedules should be established.
During construction, detailed records should be kept of: (a) charge weight,
(b) location of blast point and distance from existing structures, (c)
delays, and (d) response as indicated by vibration monitoring. For safety,
small charges should be used initially to establish a site specific
relationship between charge weight, distance, and response.

7.2-21

7.2-22

7.2-23

7.2-25

7.2-26

Section 6. GROUNDWATER CONTROL

1. APPLICATION. Excavations below the groundwater table require
groundwater control to permit construction in the dry and maintain the
stability of excavation base and sides. This is accomplished by controlling
seepage into the excavation and controlling artesian water pressures below
the bottom of the excavation.

2. METHOD. See Table 7 (modified from Reference 15, Control of Groundwater
by Water Lowering, by Cashman and Harris) for methods of controlling
groundwater, their applicability, and limitations. Wellpoints, deep wells,
and sumps are most commonly used. Figures 13(A) (from Reference 2) and
13(B) (from Reference 16, Design and Construction of Dry Docks, by
Mazurkiewicz) show a dewatering system using deep wells, and a two stage
well point system. Figures 13(C) and 13(D) (from Reference 16) shows
details of a wellpoint system, and a deep well with electric submersible
pump. See Figure 14 (from Reference 2) for applicable limits of dewatering
methods.

3. DESIGN PROCEDURE. See DM-7.1, Chapter 6 for description of design
procedures for groundwater control. For additional guidance on groundwater
control see NAVFAC P-418.

Section 7. EXCAVATION STABILIZATION, MONITORING, AND SAFETY

1. STABILIZATION. During the planning and design stage, if analyses
indicate potential slope instability, means for slope stabilization or
retention should be considered. Some methods for consideration are given in
Chapter 3.

On occasion, the complexity of a situation may dictate using very
specialized stabilization methods. These may include grouting and
injection, ground freezing, deep drainage and stabilization, such as vacuum
wells or electro-osmosis (see DM-7.3, Chapter 2), and diaphragm walls (see
DM-7.3, Chapter 3).

2. MONITORING. During excavation, potential bottom heave, lateral wall or
slope movement, and settlement of areas behind the wall or slope should be
inspected carefully and monitored if critical. Monitoring can be
accomplished by conventional survey techniques, or by more sophisticated
means such as heave points, settlement plates, extensometers or
inclinometers, and a variety of other devices. See DM-7.1, Chapter 2.

3. SAFETY. Detailed safety requirements vary from project to project. As a
guide, safety requirements are specified by OSHA, see Reference 17, Public
Law 91-596. A summary of the 1980 requirements follows:

a. OSHA Rules.

(1) Banks more than 4 feet high shall be shored or sloped to the
angle of repose where a danger of slides or cave-ins exists as a result of
excavation.

7.2-27

7.2-31

7.2-32

(2) Sides of trenches in unstable or soft material, 4 feet or more
in depth, shall be shored, sheeted, braced, sloped, or otherwise supported
by means of sufficient strength to protect the employee working within them.

(3) Sides of trenches in hard or compact soil, including
embankments, shall be shored or otherwise supported when the trench is more
than 4 feet in depth and 8 feet or more in length. In lieu of shoring, the
sides of the trench above the 4-foot level may be sloped to preclude
collapse, but shall not be steeper than a 1-foot rise to each 1/2-foot
horizontal. When the outside diameter of a pipe is greater than 6 feet, a
bench of 4-foot minimum shall be provided at the toe of the sloped portion.

(4) Materials used for sheeting and sheet piling, bracing, shoring,
and underpinning shall be in good serviceable condition. Timbers used shall
be sound and free from large or loose knots, and shall be designed and
installed so as to be effective to the bottom of the excavation.

(5) Additional precautions by way of shoring and bracing shall be
taken to prevent slides or cave-ins when (a) excavations or trenches are
made in locations adjacent to backfilled excavations; or (b) where
excavations are subjected to vibrations from railroad or highway traffic,
operation of machinery, or any other source.

(6) Employees entering bell-bottom pier holes shall be protected by
the installation of a removable-type casing of sufficient strength to resist
shifting of the surrounding earth. Such temporary protection shall be
provided for the full depth of that part of each pier hole which is above
the bell. A lifeline, suitable for instant rescue and securely fastened to
the shafts, shall be provided. This lifeline shall be individually manned
and separate from any line used to remove materials excavated from the bell
footing.

(7) Minimum requirements for trench timbering shall be in
accordance with Table 3.

(8) Where employees are required to be in trenches 3 feet deep or
more, ladders shall be provided which extend from the floor of the trench
excavation to at least 3 feet above the top of the excavation. They shall
be located to provide means of exit without more than 25 feet of lateral
travel.

(9) Bracing or shoring of trenches shall be carried along with the
excavation.

(10) Cross braces or trench jacks shall be placed in true
horizontal position, spaced vertically, and secured to prevent sliding,
falling, or kickouts.

(11) Portable trench boxes or sliding trench shields may be used
for the protection of employees only. Trench boxes or shields shall be
designed, constructed, and maintained to meet acceptable engineering
standards.

(12) Backfilling and removal of trench supports shall progress
together from the bottom of the trench. Jacks or braces shall be released
slowly, and in unstable soil, ropes shall be used to pull out the jacks or
braces from above after employees have cleared the trench.

7.2-34

REFERENCES

1. Clough, G.W. and Davidson, R.R., Effects of Construction on
Geotechnical Engineering, Specialty Session No. 3, Relationship Between
Design and Construction in Soil Engineering, Ninth International
Conference on Soil Mechanics and Foundation Engineering, Tokyo, 1977.

2. Departments of the Army and the Air Force, Soils and Geology,
Procedures for Foundation Design of Buildings and Other Structures
(Except Hydraulic Structures), TM 5/818-1/AFM 88-3, Chapter 7,
Washington, DC, 1979.

3. Terzaghi, K., Stability of Steep Slopes on Hard Unweathered Rock,
Norwegian Geotechnical Institute, Publication No. 50, 1963.

4. Petersen, E.V., Cave-In!, Roads and Engineering Construction,
November 1963, December 1963, January 1964.

5. Goldberg, D.T., Jaworkski, W.E., and Gordon, M.D., Lateral Support
Systems and Underpinning, Vol. II, Design Fundamentals, Vol. III.
Construction Methods, Federal Highway Administration, Report Nos.
FHWA-RD-75-129, 130, 1976.

6. Bjerrum, L., Clausen, J.F. and Duncan, J.M., Stability of Flexible
Structures, General Report, Proceedings, Fifth-International European
Conference on Soil Mechanics and Foundation Engineering, Vol. 11, 1977.

7. Lambe, T.W., Braced Excavation, 1970 Specialty Conference, Lateral
Stresses in the Ground and Design of Earth Retaining Structures, June
22-24, Cornell University, ASCE, 1971.

8. Peck, R. B., Deep Excavations and Tunneling in Soft Ground,
Proceedings, Seventh International Conference on Soil Mechanics and
Foundation Engineering, State-of-the-Art Vol. 1, 1969.

9. O'Rourke, T.P., Cording, E.J. and Boscardin, M., Damage to Brick
Bearing Wall Structures Caused by Adjacent Braced Cuts and Tunnels,
Large Ground Movements, John Wiley & Sons, 1977.

10. Caterpillar Tractor Co., Handbook of Ripping, Fifth Edition, Peoria,
IL., 1975.

11. Franklin, J.A., Broch, E. and Walton, G., Logging the Mechanical
Character of Rock, Transactions, Institution of Mining and Metallurgy
January 1971.

12. Broch, E. and Franklin, J.A., The Point-load Strength Test,
International Journal Rock Mechanics and Mining Science, Vol. 9, 1972.

13. Bureau of mines, Blasting Vibrations and Their Effect on Structures,
United States Department of the Interior, 1971.

7.2-35 Change 1, September 1986

14. Hendron, A.J., Engineering of Rock Blasting on Civil Projects, Rock
Excavation Seminar Lectures, ASCE, New York, October, 1976.

15. Cashman, P.M. and Harris, E.T., Control of Groundwater by Water
Lowering, Conference on Ground Engineering, Institute of Civil
Engineers, London, 1970.

16. Mazurdiewicz, B.K., Design and Construction of Dry Docks, Trans Tech
Publications, Rockport, MA, 1980.

17. Public Law 91-596 (Williams-Steiger Act), Occupational Safety and
Health Act (OSHA) of 1970, Dec. 29, 1970.

18. Naval Facilities Engineering Command P-Publication, P-418, Dewatering
and Groundwater Control. Copies may be obtained from the U.S. Naval
Publications and Forms Center, 5801 Tabor Avenue, Philadelphia, PA
19120.

Change 1, September 1986 7.2-36

CHAPTER 2. COMPACTION, EARTHWORK, AND HYDRAULIC FILLS

Section 1. INTRODUCTION

1. SCOPE. This chapter concerns design and construction of compacted fills
and performance of compacted materials. Compaction requirements are given
for various applications and equipment. Earthwork control procedures end
analysis of control test data are discussed. Guidance on hydraulic fills is
also included.

2. RELATED CRITERIA. For additional criteria concerned with compaction and
earthwork operations, consult the following sources:

Subject Source

Pavements NAVFAC DM-5.04
Flexible Pavement Design for Airfield NAVFAC DM-21.03
Dredging NAVFAC DM-26.03
Types of Dredging Equipment NAVFAC DM-38.02

3. PURPOSE OF COMPACTION.

(1) Reduce material compressibility.
(2) Increase material strength.
(3) Reduce permeability.
(4) Control expansion.
(5) Control frost susceptibility.

4. APPLICATIONS. The principal uses of compacted fill include support of
structures or pavements, embakments for water retention or for lining
reserviors and canals, and backfill surrounding structures or buried
utitlities.

5. TYPES OF FILL.

a. Controlled Compacted Fills. Properly placed compacted fill will be
more rigid and uniform and have greater strength than most natural soils.

b. Hydraulic Fills. Hydraulic fills cannot be compacted during
placement and therefore it is important that the source materials be
selected carefully.

c. Uncontrolled Fills. These consist of soils or industrial and
domestic wastes, such as ashes, slag, chemical wastes, building rubble, and
refuse. Use of ash, slag, and chemical waste is stringently controlled and
current Environmental Protection Agency or other appropriate regulations
must be considered.

7.2-37 Change 1, September 1986

Section 2. EMBANKMENT CROSS-SECTION DESIGN

1. INFLUENCE OF MATERIAL TYPE. Table 1 lists some typical properties of
compacted soils which may be used for preliminary analysis. For final
analysis engineering property tests are necessary.

a. Utilization. See Table 2 for relative desirability of various soil
types in earth fill dams, canals, roadways and foundations. Although
practically any nonorganic insoluble soil may be incorporated in an
embankment when modern compaction equipment and control standards are
employed, the following soils may be difficult to use economically:

(1) Fine-grained soils may have insufficient shear strength or
excessive compressibility.

(2) Clays of medium to high plasticity may expand if placed under
low confining pressures and/or at low moisture contents. See DM- 7.01,
Chapter I for identification of soils susceptible to volume expansion.

(3) Plastic soils with high natural moisture are difficult to
process for proper moisture for compaction.

(4) Stratified soils may require extensive mixing of borrow.

2. EMBANKMENTS ON STABLE FOUNDATION. The side slopes of fills not
subjected to seepage forces ordinarily vary between 1 on 1-1/2 and 1 on 3.
The geometry of the slope and berms are governed by requirements for erosion
control and maintenance. See DM-7.01, Chapter 7 for procedures to calculate
stability of embankments.

3. EMBANKMENTS ON WEAK FOUNDATIONS. Weak foundation soils may require
partial or complete removal, flattening of embankment slopes, or
densification. Analyze cross-section stability by methods of DM-7.01,
Chapter 7. See DM-7.03, Chapter 2 for methods of deep stabilization, and
Chapter 3 for special problem soils.

4. EMBANKMENT SETTLEMENT. Settlement of an embankment is caused by
foundation consolidation, consolidation of the embankment material itself,
and secondary compression in the embankment after its completion.

a. Foundation Settlement. See DM-7.01, Chapter 5 for procedures to
decrease foundation settlement or to accelerate consolidation. See DM-7.03,
Chapter 1 for guidance on settlement potential under seismic conditions.

b. Embankment Consolidation. Significant excess pore pressures can
develop during construction of fills exceeding about 80 feet in height or
for lower fills of plastic materials placed wet of optimum moisture.
Dissipation of these excess pore pressures after construction results in
settlement. For earth dams and other high fills where settlement is
critical, construction pore pressures should be monitored by the methods of
DM-7.01, Chapter 2.

Change 1, September 1986 7.2-38

c. Secondary Compression. Even for well-compacted embankments,
secondary compression and shear strain can cause slight settlements after
completion. Normally this is only of significance in high embankments,
and can amount to between 0.1 and 0.2 percent of fill height in three to
four years or between 0.3 and 0.6 percent in 15 to 20 years. The larger
values are for fine-grained plastic soils.

5. EARTH DAM EMBANKMENTS. Evaluate stability at three critical stages; the
end of construction stage, steady state seepage stage, and rapid drawdown
stage. See DM-7.1, Chapter 7 for pore pressure distribution at these
stages. Seismic forces must be included in the evaluation. Requirements
for seepage cutoff and stability dictate design of cross section and
utilization of borrow materials.

a. Seepage Control. Normally the earthwork of an earth dam is zoned
with the least pervious, fine-grained soils in the central zone and
coarsest, most stable material in the shell. Analyze seepage by the methods
of DM-7.1, Chapter 6.

(1) Cutoff Trench. Consider the practicability of a positive
cutoff trench extending to impervious strata beneath the embankment and into
the abutments.

(2) Intercepting Seepage. For a properly designed and constructed
zoned earth dam, there is little danger from seepage through the embankment.
Drainage design generally is dictated by necessity for intercepting seepage
through the foundation or abutments. Downstream seepage conditions are more
critical for homogeneous fills. See DM-7.1, Chapter 6 for drainage and
filter requirements.

b. Piping and Cracking. A great danger to earth dams, particularly
those of zoned construction, is the threat of cracking and piping. Serious
cracking may result from tension zones caused by differences in
stress-strain properties of zoned material. See Figure 1 (Reference 1,
Influence of Soil Properties and Construction Methods on the Performance of
Homogeneous Earth Dams, by Sherard) for classification of materials
according to resistance to piping or cracking. Analyze the embankment
section for potential tension zone development. Place an internal drainage
layer immediately downstream of the core to control seepage from possible
cracking if foundation settlements are expected to be high.

c. Dispersive soil. Dispersive clays should not be used in dam
embankments. Determine the dispersion potential using Table 3 or the method
outlined in Reference 2, Pinhole Test for Identifying Dispersive Soils, by
Sherard, et al. A hole through a dispersive clay will increase in size as
water flows through (due to the breakdown of the soil structure), whereas
the size of a hole in a non-dispersive clay would remain essentially
constant. Therefore, dams constructed with dispersive clays are extremely
susceptible to piping.

7.2-41

7.2-42

7.2-43

TABLE 3
Clay Dispersion Potential

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

*Percent Dispersion

Dispersive Tendency

*))))))))))))))))))))))))))))))))))))*)))))))))))))))))))))))))))))))))))))))))))*

Over 40

Highly Dispersive (do not use)

15 to 40

Moderately Dispersive

0 to 15

Resistant to Dispersion

*))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

*The ratio between the fraction finer than 0.005 mm in a soil-water suspension

that has been subjected to a minimum of mechanical agitation, and the total

fraction finer than 0.005 mm determined from a regular hydrometer test x 100.

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-44

Section 3. COMPACTION REQUIREMENTS AND PROCEDURES

1. COMPACTION REQUIREMENTS.

a. Summary. See Table 4 for a summary of compaction requirements of
fills for various purposes. Modify these to meet conditions and materials
for specific projects.

b. Specification Provisions. Specify the desired compaction result.
State the required density, moisture limits, and maximum lift thickness,
allowing the contractor freedom in selection of compaction methods and
equipment. Specify special equipment to be used if local experience and
available materials so dictate.

2. COMPACTION METHODS AND EQUIPMENT. Table 5 lists commonly used
compaction equipment with typical sizes and weights and guidance on use and
applicability.

3. INFLUENCE OF MATERIAL TYPE.

a. Soils Insensitive to Compaction Moisture. Coarse-grained, granular
well-graded soils with less than 4 percent passing No. 200 sieve (8 percent
for soil of uniform gradation) are insensitive to compaction moisture.
(These soils have a permeability greater than about 2 x 10

-3

fpm.) Place

these materials at the highest practical moisture content, preferably
saturated. Vibratory compaction generally is the most effective procedure.
In these materials, 70 to 75 percent relative density can be obtained by
proper compaction procedures. If this is substantially higher than Standard
Proctor maximum density, use relative density for control. Gravel, cobbles
and boulders are insensitive to compaction moisture. Compaction with smooth
wheel vibrating rollers is the most effective procedure. Use large scale
tests, as outlined in Reference 3, Control of Earth Rockfill for Oroville
Dam, by Gordon and Miller.

b. Soils Sensitive to Compaction Moisture. Silts and some silty sands
have steep moisture-density curves, and field moisture must be controlled
Within narrow limits for effective compaction. Clays are sensitive to
moisture in that if they are too wet they are difficult to dry to optimum
moisture, and if they are dry it is difficult to mix the water in uniformly.
Sensitive clays do not respond to compaction because they lose strength upon
remolding or manipulation.

c. Effect of Oversize. Oversize refers to particles larger than the
maximum size allowed using a given mold (i.e. No. 4 for 4-inch mold, 3/4
inch for 6-inch mold, 2-inch for a 12-inch mold). Large size particles
interfere with compaction of the finer soil fraction. For normal embankment
compaction the maximum size cobble should not exceed 3 inches or 50 percent
of the compacted layer thickness. Where economic borrow sources contain
larger sizes, compaction trials should be run before approval.

7.2-45

Adjust laboratory maximum standard density (from moisture-density
relations test, see DM-7.01 Chapter 3) to provide a reference density to
which field density test results (with oversize) can be compared. Use the
following equations to adjust the laboratory maximum dry density and optimum
moisture content to values to which field test data (with oversize
particles) may be compared.

The density of oversize material is assumed as 162 pcf, obtained
from bulk specific gravity 2.60, multiplied by 62.4.

This method is considered suitable when the weight of oversize is
less than 60% by weight, for well-graded materials. For poorly graded
materials, further adjustment may be appropriate. This method is modified
after that described in Reference 4, Suggested Method for Correcting Maximum
Density and Optimum Moisture Content of Compacted Soils for Oversize
Particles, by McLeod; also see Reference 5, Scalping and Replacement Effects
on the Compaction Characteristics of Earth-Rock Mixtures, by Donaghe and
Townsend.

Section 4. EMBANKMENT COMPACTION CONTROL

1. GROUND PREPARATION.

(1) Strip all organics and any other detrimental material from the
surface. in prairie soils this may amount to removal of 2 or 3 inches of
topsoil, and in forest covered land between 2 and 5 or more feet. Only the
heavy root mat and the stumps need be removed, not the hair-like roots.

(2) Remove subsurface structures or debris which will interfere with
the compaction or the specified area use.

(3) Scarify the soil, and bring it to optimum moisture content.

Change 1, September 1986 7.2-50

(4) Compact the scarified soil to the specified density.

2. FIELD TEST SECTION. By trial, develop a definite compaction procedure
(equipment, lift thickness, moisture application, and number of passes)
which will produce the specified density. Compaction cannot be controlled
adequately by spot testing unless a well defined procedure is followed.

3. REQUIREMENTS FOR CONTROL TESTS. Perform in-place field density tests
plus sufficient laboratory moisture-density tests to evaluate compaction.
For high embankments involving seepage, settlement, or stability, perform
periodic tests for engineering properties of density test samples, e.g.,
permeability tests, shear strength tests. See DM-7.1, Chapter 3 for
laboratory moisture density test procedures and DM-7.1, Chapter 2 for field
density test methods.

a. Number of Field Density Tests. Specify the following minimum test
schedule:

(1) One test for every 500 cu yd of material placed for embankment
construction.

(2) One test for every 500 to 1,000 cu yd of material for canal or
reservoir linings or other relatively thin fill sections.

(3) One test for every 100 to 200 cu yd of backfill in trenches or
around structures, depending upon total quantity of material involved.

(4) At least one test for every full shift of compaction operations
on mass earthwork.

(5) One test whenever there is a definite suspicion of a change in
the quality of moisture control or effectiveness of compaction.

b. Field Density Test Methods. See DM-7.1, Chapter 2, for field
density test methods.

Proofrolling (spotting soft spots with a rubber-tired roller or any
loaded earth-moving equipment) may be used in conjunction with density
testing, but is practical only for extensive earthwork or pavement courses.

c. Laboratory Compaction Tests. Prior to important earthwork
operations, obtain a family of compaction curves representing typical
materials. Ideally, this family will form a group of parallel curves and
each field density test will correspond to a specific compaction curve.

During construction obtain supplementary compaction curves on field
density test samples, approximately one for every 10 or 20 field tests,
depending on the variability of materials.

4. ANALYSIS OF CONTROL TEST DATA. Compare each field determination of
moisture and density with appropriate compaction curve to evaluate
conformance to requirements.

7.2-51

a. Statistical Study. Overall analysis of control test data will
reveal general trends in compaction and necessity for altering methods.
Inevitably, a certain number of field determinations will fall below
specified density or outside specified moisture range. Tabulate field
tests, noting the percentage difference between field density and laboratory
maximum density and between field moisture and optimum.

b. Moisture Control. Close moisture control is evidenced if two-thirds
of all field values fall in a range +/- 1 percent about the median moisture
content specified. Erratic moisture control is evidenced if approximately
two-thirds of all field values fall in a range +/- 3 percent about the
median moisture content specified. To improve moisture control, blend
materials from wet and dry sections of borrow area.

c. Compactive Effort. Suitable compaction methods are being utilized
if approximately two-thirds of all field densities fall in a range of +/- 3
percent about the percent maximum density required. Insufficient or erratic
compaction is evidenced if approximately two-thirds of all field values fall
in a range of +/- 5 percent about the percent maximum density required. To
improve compaction, consider methods for more uniform moisture control,
alter the number of coverages, weights, or pressures of compaction
equipment.

d. Overcompaction. A given compactive effort yields a maximum dry
density and a corresponding optimum moisture content. If the compactive
effort is increased, the maximum dry density increases but the corresponding
optimum moisture content decreases. Thus, if the compactive effort used in
the field is higher than that used in the laboratory for establishing the
moisture density relationship, the soil in the field may be compacted above
its optimum moisture content, and the strength of the soil may be lower even
though it has been compacted to higher density. This is of particular
concern for high embankments and earth dams. For further guidance see
Reference 6, Stabilization of Materials by Compaction, by Turnbull and
Foster.

5. INDIRECT EVALUATION OF COMPACTION IN DEEP FILLS. The extent of
compaction accomplished is determined by comparing the results from standard
penetration tests and cone penetration tests before and after treatment
(DM-7.1, Chapter 2).

6. PROBLEM SOILS. The compaction of high volume change soils requires
special treatment. See DM-7.3, Chapter 3.

Section 5. BORROW EXCAVATION

1. BORROW PIT EXPLORATION

a. Extent. The number and spacing of borings or test pits for borrow
exploration must be sufficient to determine the approximate quantity and
quality of construction materials within an economical haul distance from
the project. For mass earthwork, initial exploration should be on a
200-foot grid. If variable conditions are found during the initial
explorations, intermediate borings or test pits should be done.
Explorations should develop the following information:

7.2-52

(1) A reasonably accurate subsurface profile to the anticipated
depth of excavation.

(2) Engineering properties of each material considered for use.

(3) Approximate volume of each material considered for use.

(4) Water level.

(5) Presence of salts, gypsums, or undesirable minerals.

(6) Extent of organic or contaminated soils, if encountered.

2. EXCAVATION METHODS.

a. Equipment. Design and efficiency of excavation equipment improves
each year. Check various construction industry publications for
specifications.

b. Ripping and Blasting. Determine rippability of soil or rock by
borings (RQD and core recovery, see DM-7.01, Chapters 1 and 2), geophysical
exploration, and/or trial excavation.

3. UTILIZATION OF EXCAVATED MATERIALS. In the process of earthmoving there
may be a reduction of the volume ("shrinkage") because of waste and
densification, or an increase of volume ("swell") in the case of rock or
dense soils, because the final density is less than its original density.

a. Borrow Volume. Determine total borrow volume, V

required

for compacted fill as follows:

(1) Compacted Volume. The volume of borrow soil required should be
increased according to the volume change indicated above. A "shrinkage"
factor of 10 to 15 percent may be used for estimating purposes.

(2) Exclusions. A large percentage of cobble size material will
increase the waste, because sizes larger than 3 inches are generally
excluded from compacted fill.

b. Rock Fill.

(1) Maximum Expansion. Maximum expansion ("swell") from in situ
conditions to fill occurs in dense, hard rock with fine fracture systems
that

7.2-53 Change 1, September 1986

breaks into uniform sizes. Unit volume in a quarry will produce
approximately 1.5 volumes in fill.

(2) Minimum Expansion. Minimum expansion occurs in porous, friable
rock that breaks into broadly graded sizes with numerous spalls and fines.
Unit volume in quarry will produce approximately 1.1 volumes in fill.

Section 6. HYDRAULIC AND UNDERWATER FILLS

1. GENERAL. Where large quantities of soil must be transported and ample
water is available, hydraulic methods are economical. The choice of methods
for placing hydraulic fill is governed by the type of equipment available,
accessibility of borrow, and environmental regulations; see Table 6
(Reference 7, Control for Underwater Construction, by Johnson, et al.).
Removal or placement of soil by hydraulic methods must conform to applicable
water pollution control regulations.

2. PLACEMENT METHODS. Placement, either under water or on land, should be
done in a manner that produces a usable area with minimum environmental
impact.

a. Deep Water Placement (over 75 feet). Most deep water placement is
by bottom dump scows and is unconfined, with no control on turbidity, except
by the rate of dumping.

b. Shallow Water Placement. Placement by pipeline, by mechanical
equipment, or by side dumping from deck scows are the most common methods in
shallow water. Sheet pile containment, silt "curtains", or dikes are
required to minimize lateral spreading and environmental impact. Where
lateral spreading is not desired and steeper side slopes are needed, control
the method of placement or use a mixed sand and gravel fill material. With
borrow containing about equal amounts of sand and gravel, underwater slopes
as steep as 1:3 or 1:2-3/4 may be achieved by careful placement. To confine
the fill, provide berms or dikes of the coarsest available material or stone
on the fill perimeter. Where rock is placed underwater, sluice voids with
sand to reduce compressibility and possible loss of material into the rock.

c. Land Placement. On land, hydraulic fills are commonly placed by
pipeline or by mechanical procedures (i.e. clam shell, dragline, etc.).
Dikes with adjustable weirs or drop inlets to control the quality of return
water are used for containment.

3. PERFORMANCE OF HYDRAULIC FILLS.

a. Coarse-Grained Fills. The most satisfactory hydraulically placed
fills are those having less than 15 percent non-plastic fines or 10 percent
plastic fines because they cause the least turbidity during placement, drain
faster, and are more suitable for structural support than fine-grained
material. Relative densities of 50 to 60 percent can be obtained without
compaction. Bearing values are in the range of 500 to 2000 pounds per
square foot depending on the level of permissible settlement. Density,
bearing and

Change 1, September 1986 7.2-54

TABLE 6
Methods of Fill Placement Underwater

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

Methods Characteristics

*))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Bottom-dump scows 1. Limited to minimum depths of about 15 ft.

because of scow and tug drafts.

2. Rapid; quick discharge entraps air and

minimizes segregation.

*))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Deck scows 1. Usable in shallow water.

2. Unloading is slow 9 by dozer, clamshell, or

hydraulic jets.

3. Inspection of material being placed may be

difficult.

*))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

Dumping at land edge of 1. Fines in material Placed below water tend to

fill and pushing material separate and accumulate in front of advancing

material into water by fill.

bulldozer

2. Work arrangement should result in central

portion being in advance of side portions to

displace sideways any soft bottom materials.

3. In shallow water, bulldozer blade can shove

materials downward to assist displacement of

soft materials.

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-55

resistance to seismic liquefaction may be increased substantially by
vibroprobe methods. See DM-7.3, Chapter 2.

b. Fine-Grained Fills. Hydraulically placed, bottom silts and clays
such as produced by maintenance dredging will initially be at very high
water contents. Depending on measures taken to induce surface drainage, it
will take approximately 2 years before a crust sufficient to support light
equipment is formed and the water content of the underlying materials
approaches the liquid limit. Placing 1 to 3 feet of additional granular
borrow will improve these areas rapidly so that they can support surcharge
fills, with or without vertical sand drains to accelerate consolidation.
Care must be exercised in applying the surcharge so that the shear strength
of the soil is not exceeded.

4. CONSOLIDATION OF HYDRAULIC FILLS. If the coefficient of permeability of
a hydraulic fill is less than 0.002 feet per minute, the consolidation time
for the fill will be long and prediction of the behavior of the completed
fill will be difficult. For coarse-grained materials, fill consolidation
and strength build-up will be rapid and reasonable strength estimates can be
made. Where fill and/or foundation soils are fine-grained, it may be
desirable to monitor settlement and pore water pressure dissipation if
structures are planned. Settlement plates may be placed both on the
underlying soil and within the fill to observe settlement rates and amounts.

7.2-56

REFERENCES

1. Sherard, J.L., Influence of Soil Properties and Construction Methods on
the Performance of Homogeneous Earth Dams, Technical Memorandum 645,
U.S. Department of the Interior, Bureau of Reclamation.

2. Sherard, J.L., Dunnigan, L.P., Becker, R.S., and Steele, E.S., Pinhole
Test for Identifying Dispersive Soils, Journal of the Geotechnical
Engineering Division, ASCE, Vol. 102, No. GT1, 1976.

3. Gordori, B.B., Miller, R.K., Control of Earth and Rockfill for Oroville
Dam, Journal of the Geotechnical Engineering Division, ASCE, Vol. 92,
No. SM3, 1966.

4. McLeod, N.W., Suggested Method for Correcting Maximum Density and
Optimum Moisture Content of Compacted Soils for Oversize Particles,
Special Procedures for Testing Soil and Rock for Engineering Purposes,
ASTM STP 479, ASTM, 1970.

5. Donaghe, R.T., and Townsend, F.C., Scalping and Replacement Effects on
the Compaction Characteristics of Earth-Rock Mixtures, Soil Specimen
Preparation for Laboratory Testing, ASTM STP 599, ASTM, 1976.

6. Turnbull, W.J. and Foster, C.R., Stabilization of Materials by
Compaction, Journal of the Soil Mechanics and Foundation Division, ASCE,
Vol. 82, No. SM2, 1956.

7. Johnson, S.J., Compton, J.R., and Ling, S.C., Control for Underwater
Construction, Underwater Sampling, Testing, and Construction Control,
ASTM STP 501, ASTM, 1972.

8. Naval Facilities Engineering Command

Design Manuals (DM)
DM- 5.04 Pavements
DM-21.03 Flexible Pavement Design for Airfields
DM-26.03 Coastal Sedimentation and Dredging
DM-38.02 Dredging Equipment

Copies may be obtained from the U.S. Naval Publications and Forms
Center, 5801 Tabor Avenue, Philadelphia, PA 19120.

7.2-57 Change 1, September 1986

PAGE 58 INTENTIONALLY BLANK

CHAPTER 3. ANALYSIS OF WALLS AND RETAINING STRUCTURES

Section 1. INTRODUCTION

1. SCOPE. Methods of determining earth pressures acting on walls and
retaining structures are summarized in this chapter. Types of walls
considered include concrete retaining walls and gravity walls that move
rigidly as a unit, braced or tied bulkheads of thin sheeting that deflect
according to the bracing arrangement, and double-wall cofferdams of thin
sheeting to confine earth or rock fill.

2. RELATED CRITERIA. Additional criteria relating to the design and
utilization of walls appear in the following sources:

Subject Source

Application of Bulkheads and Cofferdams to
Waterfront Construction NAVFAC DM-25.04

Structural Design of Retaining Walls NAVFAC DM-2 Series

Section 2. COMPUTATION OF WALL PRESSURES

1. CONDITIONS. The pressure on retaining walls, bulkheads, or buried
anchorages is a function of the relative movement between the structure and
the surrounding soil.

a. Active State. Active earth pressure occurs when the wall moves away
from the soil and the soil mass stretches horizontally sufficient to
mobilize its shear strength fully, and a condition of plastic equilibrium is
reached. (See Figure 1 from Reference 1, Excavations and Retaining
Structures, by the Canadian Geotechnical Society.) The ratio of the
horizontal component or active pressure to the vertical stress caused by
weight of soil is the active pressure coefficient (K

). The active

pressure coefficient as defined above applies only to cohesionless soils.

b. Passive State. Passive earth pressure occurs when a soil mass is
compressed horizontally, mobilizing its shear resistance fully (see Figure
1). The ratio of the horizontal component of passive pressure to the
vertical stress caused by the weight of the soil is the passive pressure
coefficient (K

). The passive coefficient, as defined here, applies only

the cohesionless soil. A soil mass that is neither stretched nor compressed
is said to be in an at-rest state. The ratio of lateral stress to vertical
stress is call the at-rest coefficient (K

7.2-59 Change 1, September 1986

2. COMPUTATION OF ACTIVE AND PASSIVE PRESSURES. See Figure 2 for formulas
for active and passive pressures for the simple case on a frictionless
vertical face with horizontal ground surface. Three basic conditions
required for validity of the formulas are listed in Figure 2. Under these
conditions the failure surface is a plane and the formulas represent
pressures required for equilibrium of the wedge shaped failure mass.

The intensity of pressures applied depends on wall movements, as these
control the degree of shear strength mobilization in surrounding soil. (See
Figure 1 for the magnitude of the movement necessary for active condition to
exist.) Wall friction and wall vertical movements also affect the
passive and active pressures.

The effect of wall friction on active pressures is small and ordinarily is
disregarded except in case of a settling wall where it can be very
significant. The effect of wall friction on passive pressures is large, but
definite movement is necessary for mobilization of wall friction. (See
Table 1 for typical ultimate friction factors and adhesion between wall and
backfill.) In the absence of specific test data, use these values in
computations that include effects of wall friction.

Unless a wall is settling, friction on its back acts upward on the active
wedge (angle [delta] is positive, see Figure 5), reducing active pressures.
Generally, wall friction acts downward against the passive wedge (angle
[delta] is negative), resisting its upward movement and increasing passive
pressures.

a. Uniform Backfill, No Groundwater. Compute active and passive
pressures by methods from Figure 2.

b. Sloping Backfill, No Groundwater, Granular Soil, Smooth Wall.
Compute active and passive pressures by methods from Figure 3. Use Figure 4
to determine the position of failure surface for active and passive wedge.

c. Sloping Wall, Granular Soil With Wall Friction. Use Figure 5
(Reference 2, Tables for the Calculation of the Passive Pressure, Active
Pressure and Bearing Capacity of Foundations, by Caquot and Kerisel) to
compute active and passive earth pressure coefficients.

d. Sloping Backfill, Granular Soil with Wall Friction. Use Figure 6
(Reference 2) to compute active and passive earth pressure coefficient.

e. Uniform Backfill, Static Groundwater. Compute active earth and
water pressures by formulas in Figure 7.

f. General Formula for Coefficients of Passive and Active Earth
Pressure. Use Figure 8 for sloping wall with friction and sloping backfill.

g. Stratified Backfill, Sloping Groundwater Level. When conditions
include layered soil, irregular surcharge, wall friction, and sloping
groundwater level, determine active pressures by trial failure wedge. (See
Figure 7.) Trial wedge is bounded by a straight failure plane or a series
of straight segments at different inclination in each stratum. Commence
the analysis with failure plane oriented at the angle shown in Figure 4.

7.2-61 Change 1, September 1986

TABLE 1
Ultimate Friction Factors and Adhesion for Dissimilar Materials

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))0))))))))))))))0)))))))))),

Friction

angle

Interface Materials

factor,

[delta]

tan [delta]

degrees

/)))))))))))))))))))))))))))))))))))))))))))))))))))))))3))))))))))))))3))))))))))1

Mass concrete on the following foundation materials:

Clean sound rock..................................

0.70

Clean gravel, gravel-sand mixtures, coarse sand...

0.55 to 0.60

29 to 31

Clean fine to medium sand, silty medium to coarse

sand, silty or clayey gravel....................

0.45 to 0.55

24 to 29

Clean fine sand, silty or clayey fine to medium

sand............................................

0.35 to 0.45

19 to 24

Fine sandy silt, nonplastic silt..................

0.30 to 0.35

17 to 19

Very stiff and hard residual or preconsolidated

clay............................................

0.40 to 0.50

22 to 26

Medium stiff and stiff clay and silty clay........

0.30 to 0.35

17 to 19

(Masonry on foundation materials has same friction

factors.)

Steel sheet piles against the following soils:

Clean gravel, gravel-sand mixtures, well-graded

rock fill with spalls...........................

0.40

Clean sand, silty sand-gravel mixture, single size

hard rock fill..................................

0.30

Silty sand, gravel or sand mixed with silt or clay

0.25

Fine sandy silt, nonplastic silt..................

0.20

Formed concrete or concrete sheet piling against the

following soils:

Clean gravel, gravel-sand mixture, well-graded

rock fill with spalls...........................

0.40 to 0.50

22 to 26

Clean sand, silty sand-gravel mixture, single size

hard rock fill..................................

0.30 to 0.40

17 to 22

Silty sand, gravel or sand mixed with silt or clay

0.30

Fine sandy silt, nonplastic silt..................

0.25

Various structural materials:

Masonry on masonry, igneous and metamorphic rocks:

Dressed soft rock on dressed soft rock..........

0.70

Dressed hard rock on dressed soft rock..........

0.65

Dressed hard rock on dressed hard rock..........

0.55

Masonry on wood (cross grain).....................

0.50

Steel on steel at sheet pile interlocks...........

0.30

/)))))))))))))))))))))))))))))))))))))))))))))))))))))))3))))))))))))))2))))))))))1

Interface Materials (Cohesion)

Adhesion c

(psf)

/)))))))))))))))))))))))))))))))))))))))))))))))))))))))3)))))))))))))))))))))))))1

Very soft cohesive soil (0 - 250 psf)

0 - 250

Soft cohesive soil (250 - 500 psf)

250 - 500

Medium stiff cohesive soil (500 - 1000 psf)

500 - 750

Stiff cohesive soil (1000 - 2000 psf)

750 - 950

Very stiff cohesive soil (2000 - 4000 psf)

950 - 1,300

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-63 Change 1, September 1986

7.2-69

Compute resultant passive force by trial failure wedge analysis.
(See Figure 9). When wall friction is included, compute pressures from a
failing mass bounded by a circular arc and straight plane. Determine
location of passive resultant by summing moments about toe of wall of all
forces on that portion of the failing mass above the circular arc.
Depending on complexity of cross section, distribute passive pressures to
conform to location of resultant, or analyze trial failure surfaces at
intermediate heights in the passive zone. When wall friction is neglected,
the trial failure surface is a straight plane. See Figure 2.

(1) Simple Cross Section. For a simple cross section behind a
wall, analyze the trial failure plane extending upward from the lowest point
of the active zone on the wall. Determine the location of the active
resultant by summing moments of all forces on the wedge about toe of wedge.
Distribute active pressures to conform to the location of resultant.

(2) Complicated Cross Section. For complicated cross sections,
analyze trial wedges at intermediate heights above the base of the active
zone to determine pressure distribution in more detail. Force acting on an
increment of wall height equals difference in resultant forces for wedges
taken from the top and bottom of that increment.

3. EFFECT OF GROUNDWATER CONDITIONS. Include in pressure computations the
effect of the greatest unbalanced water head anticipated to act across the
wall.

a. General Conditions. For a major structure, analyze seepage and
drainage effect by flow net procedures. Uplift pressures influencing wall
forces are those acting on failure surface of active or passive wedge.
Resultant uplift force on failure surface determined from flow net is
applied in force diagram of the failure wedge. See vector U, the resultant
water force, in Figures 7 and 9.

b. Static Differential Head. Compute water pressures on walls as shown
in top panel of Figure 10.

c. Rainfall on Drained Walls. For cohesionless materials, sustained
rainfall Increases lateral force on wall 20 to 40 percent over dry backfill,
depending on backfill friction angle. The center panel of Figure 10
(Reference 3, Contribution to the Analysis of Seepage Effects in Backfills,
by Gray) shows flow net set up by rainfall behind a wall with vertical
drain. This panel gives the magnitude of resultant uplift force on failure
wedge for various inclinations of failure plane to be used in analysis of
the active wedge.

d. Seepage Beneath Wall. See bottom panel of Figure 10 (Reference 4,
The Effect of Seepage on the Stability of Sea Walls, by Richart and
Schmertmann) for correction to be applied to active and passive pressures in
cohesionless material for steady seepage beneath a wall.

4. SURCHARGE LOADING. For the effects of surcharge loading, see Figures 7
and 9.

7.2-70

a. Point Load and Live Load. Use Figure 11 (Reference 5, Anchored
Bulkheads, based on the work by Terzaghi) to compute lateral pressure on
wall due to point load and line loads; this assumes an unyielding rigid wall
and the lateral pressures are approximately double the values obtained by
elastic equations. The assumption of an unyielding rigid wall is
conservative and its applicability should be evaluated for each specific
wall.

b. Uniform Loading Area. For uniform surcharge loading lateral stress
can be computed by treating the surcharge as if it were backfill and
multiplying the vertical stress at any depth by the appropriate earth
pressure coefficient.

c. Uniform Rectangular Surcharge Loading. For the effect of this
loading see Figure 12 (see Reference 6, Lateral Support Systems and
Underpinning, 2 Volume 1, Design and Construction (Summary), by Goldberg,
et al.). If the construction procedures are such that the wall will move
during the application of live loads, then the pressure calculated from
Figure 12 will be conservative.

d. Practical Considerations. For design purposes, it is common to
consider a distributed surface load surcharge on the order of 300 psf to
account for storage of construction materials and equipment. This surcharge
is usually applied within a rather limited work area of about 20 feet to 30
feet from the wall and is also intended to account for concentrated loads
from heavy equipment (concrete trucks, cranes, etc.) located more than about
20 feet away. If such equipment is anticipated within a few feet of the
wall, it must be accounted for separately.

5. WALL MOVEMENT. For the effect of wall movement on the earth pressure
coefficients, see Figure 1.

a. Wall Rotation. When the actual estimated wall rotation is less than
the value required to fully mobilize active or passive conditions, adjust
the earth pressure coefficients by using the diagram on the upper right hand
corner of Figure 1. Relatively large movements are required to mobilize the
passive resistance. A safety factor must be applied to the ultimate passive
resistance in order to limit movements.

b. Wall Translation. Wall uniform translation required to immobilize
ultimate passive resistance or active pressure is approximately equivalent
to movement of top of wall based on rotation criteria given in Figure 1.

c. Internally Braced Flexible Wall. Sheeting on cuts rigidly braced
at the top undergoes insufficient movement to produce fully active
conditions, Horizontal pressures are assumed to be distributed in a
trapezoidal diagram. (See Section 4.) The resultant force is higher than
theoretical active force. For clays, the intensity and distribution of
horizontal pressures depend on the stability number N

= [gamma] H/c.

(See Section 4.)

d. Tied Back Walls. Soil movement associated with prestressed tied back
walls is usually less than with internally braced flexible walls, and design
pressures are higher. (See Section 4.)

7.2-73

7.2-75

e. Restrained Walls. If a wall is prevented from even slight movement,
then the earth remains at or near the value of at-rest conditions. The
coefficient of earth pressure at-rest, K

, for normally consolidated

cohesive or granular soils is approximately:

= 1-sin [theta]'

where: [theta]' = effective friction angle

Thus for [theta]' = 300, K

= 0.5.

For over-consolidated soils and compacted soils the range of K

may be on the order of 1.0. In cohesionless soils, full at-rest pressure
will occur only with the most rigidly supported wall. In highly plastic
clays, soil may creep, and if wall movement is prevented, at-rest conditions
may redevelop even after active pressures are established.

f. Basement and Other Below Grade Walls. Pressure on walls below grade
may be computed based on restraining conditions that prevail, type of
backfill, and the amount of compaction.

6. EFFECT OF CONSTRUCTION PROCEDURES.

a. Staged Construction. As earth pressures are influenced by wall
movement, it is important to consider each stage of construction, especially
with regard to brace placement and its effects.

b. Compaction. Compaction of backfill in a confined wedge behind the
wall tends to increase horizontal pressures beyond those represented by
active or at-rest values. For guidance on horizontal pressure computations
associated with the compaction of granular soil, see Figure 13 (after
Reference 7, Retaining Wall Performance During Backfilling, by Ingold).

Clays and other fine-grained soils, as well as granular soils, with
considerable amount of clay and silt (>/=15%) are not normally used as
backfill material. Where they must be used, the earth pressure should be
calculated on the basis of "at-rest" conditions or higher pressure with due
consideration to potential poor drainage conditions, swelling, and frost
action.

c. Hydraulic Fills. Active pressure coefficients for loose hydraulic
fill materials range from about 0.35 for clean sands to 0.50 for silty fine
sands. Place hydraulic fill by procedures which permit runoff of wash water
and prevent building up large hydrostatic pressures. For further guidance
see discussion on dredging in DM-7.3, Chapter 3.

7. EARTHQUAKE LOADING. The pressure during earthquake loading can be
computed by the Coulomb theory with the additional forces resulting from
ground acceleration. For further guidance on the subject see Reference 8,
Design of Earth Retaining Structures for Dynamic Loads, by Seed and Whitman.
A synopsis of some material from this Reference follows:

7.2-76

7.2-77

(1) A simple procedure for determining the lateral force due to an
earthquake is to compute the initial static pressure and add to it the
increase in pressure from ground motion. For a vertical wall, with
horizontal backfill slope, and [theta] of 35 deg., (which may be assumed for
most practical cases involving granular fill), the earth pressure
coefficient for dynamic increase in lateral force can be approximated as 3/4
k

, k

being the horizontal acceleration in g's. The combined effect of

static and dynamic force is:

= 1/2 [gamma] H

+ 3/8 [gamma] H

Assume the dynamic lateral force P

= 3/8 [gamma]

acts at

0.6 H above the wall base. Effect of liquefaction is considered in DM-7.3,
Chapter 1.

(2) For other soil and wall properties, the combined resultant active
force:

For modified slope [beta]* and [theta]*, obtain KA([beta]*,
[theta]*) from the applicable figures 3 through 8. Determine F from Figure
14. Dynamic pressure increment [W-DELTA]P

can be obtained by subtracting

(also to be determined from Figures 3, 7, or 8 for given [beta] and

[theta] values) from P

. The resultant force will vary in its location

depending on wall movement, ground acceleration, and wall batter. For
practical purposes it may be applied at 0.6 H above the base.

(3) Unless the wall moves or rotates sufficiently, pressures greater
than active case will exist and the actual lateral pressures may be as large
as three times the value derived from Figure 14. In such situations,
detailed analysis using numerical techniques may be desirable.

(4) Under the combined effect of static and earthquake load a factor
of safety between 1.1 and 1.2 is acceptable.

(5) In cases where soil is below water, add the hydrodynamic pressure
computed based on:

)z = 1.5 k

[gamma]

(h [multiplied by] z)

1/2

7.2-78

7.2-79

where: P

= hydrodynamic pressure at depth z below water surface

[gamma]

= unit weight of water

h = depth of water

z = depth below the water surface

(6) Add the other inertia effect of the structure itself for
calculating the required structural strength. An optimum design is to
select the thinnest section with the largest bending and shear resistance
(i.e. most flexible).

(7) When applying this earthquake loading analysis to existing earth
retaining structures, particularly where high groundwater levels exist, it
may be found that resulting safety factor is less than 1.1. In such cases,
proposed corrective measures must be submitted to NAVFAC HQ for review and
approval.

8. FROST ACTION. Lateral forces due to frost action are difficult to
predict and may achieve high values.

Backfill materials such as silts and clayey silts (CL, MH, ML, OL) are frost
susceptible, and will exert excessive pressure on wall if proper precautions
are not taken to curb frost. Swelling pressures may be exerted by clays of
high plasticity (CH). Under these conditions, design for active pressures
is inadequate, even for yielding walls, as resulting wall movement is likely
to be excessive and continuous. Structures usually are not designed to
withstand frost generated stresses. Instead, provisions should be made so
that frost related stresses will not develop or be kept to a minimum. Use
of one or more of the following may be necessary:

(i) Permanently isolate the backfill from sources of water either by
providing a very permeable drain or a very impermeable barrier.

(ii) Provide previous backfill and weep holes. (See DM-7.1, Chapter 6
for the illustration on complete drainage and prevention of frost thrust.)

(iii) Provide impermeable soil layer near the soil surface, and grade
to drain surface water away from the wall.

9. SWELLING ACTION. Expansion of clay soils can cause very high pressures
on the back of a retaining structure. Clay backfills should be avoided
whenever possible. Swelling pressures may be evaluated based on
laboratory tests and wall designed to withstand swelling pressures.
Providing granular non-expansive filter between the clay fill and back of
wall diminishes swelling pressures and significantly limits access to
moisture. Guidance on soil stabilization methods for control of heave are
given in DM-7.3, Chapter 3. Complete drainage (see DM-7.1, Chapter 6) is
one of the techniques to control heave.

10. SELECTION OF STRENGTH PARAMETERS. The choice of strength parameters
is governed by the soil permeability characteristics, boundary drainage and
loading conditions, and time.

7.2-81

a. Saturated Cohesive Soils. For saturated cohesive soils of low
permeability, where sufficient time is not available for complete drainage,
use undrained shear strength, and total stress for earth pressure
computations. Such condition will exist during, and immediately after
completion of construction.

b. Coarse-grained Soils. In coarse-grained soils such as sand, which
have high permeability, use effective stress strength parameter [theta]',
for earth pressure computations. Also, where sufficient time is available
for the dissipation of pore pressure in less than pervious soil, use
effective stress strength parameters c' and [theta]'. In this case, pore
pressure is hydrostatic and can be estimated fairly accurately.

In soils such as silt and clayey sand, where partial drainage
occurs during the time of construction, perform analysis for limiting
conditions, i.e. effective stress with [theta]' only, total stress with c,
and design for the worst case.

Section 3. RIGID RETAINING WALLS

1. GENERAL CRITERIA. Rigid retaining walls are those that develop their
lateral resistance primarily from their own weight. Examples of rigid
structures are concrete gravity walls, thick concrete slurry walls, gabion
walls, and some reinforced earth walls reinforced for limited movements.
Theoretical wall pressures are discussed in Section 2. Requirements for
resistance against overturning and sliding of four principal wall types are
given in Figure 15. Evaluate overall stability against deep foundation
failure. (See DM-7.1, Chapter 7.) Determine allowable bearing pressures on
the base of the wall (see Chapter 4).

a. Sliding Stability. Place the base at least 3 ft below ground
surface in front of the wall and below depth of frost action, zone of
seasonal volume change, and depth of scour. Sliding stability must be
adequate without including passive pressure at the toe. If insufficient
sliding resistance is available, increase base width, provide pile
foundation or, lower base of wall and consider passive resistance below
frost depth. If the wall is supported by rock or very stiff clay, a key may
be installed below the foundation to provide additional resistance to
sliding (see Figure 15).

b. Settlement and Overturning. For walls on relatively incompressible
foundations, apply overturning criteria of Figure 15. If foundation is
compressible, compute settlement by methods of DM-7.1, Chapter 5 and
estimate tilt of rigid wall from the settlement. If the consequent tilt
will exceed acceptable limits, proportion the wall to keep the resultant
force at the middle third of base. If a wall settles such that the
resulting movement forces it into the soil which it supports, then the
lateral pressure on the active side increases substantially.

c. Overall Stability. Where retaining walls are underlain by weak
soils, the overall stability of the soil mass containing the retaining wall
should be checked with respect to the most critical surface of sliding (see
DM-7.1, Chapter 7). A minimum factor of safety of 2.0 is desirable.

7.2-82

7.2-84

d. Drainage 1. Positive drainage of backfill is desirable.
(see DM-7.1, Chapter 6 for drainage design.) As a minimum, provide weep
holes with pockets of coarse-grained material at the back of the wall. An
impervious surface layer should cover the backfill, and a gutter should be
provided for collecting runoff.

2. LOW WALLS. It has been the practice of the Naval Facilities Engineering
Command to consider walls less than 12 feet in height "low walls." For
these, knowledge of soil properties could be adequate for design, and
detailed testing and elaborate pressure computations may not be justified
economically.

a. Equivalent Fluid Pressures. Use equivalent fluid pressures of
Figure 16 (Reference 9, Soil Mechanics in Engineering Practice, by Terzaghi
and Peck) for straight slope backfill and of Figure 17 (Reference 9) for
broken slope backfill. Include dead load surcharge as an equivalent weight
of backfill. For resultant force of line load surcharge, see bottom left
panel of Figure 11. If a wall rests on a compressible foundation and moves
downward with respect to the backfill, increase pressures by 50 percent.

b. Drainage. The equivalent fluid pressures include effects of seepage
and time conditioned changes in the backfill. However, provisions should
be made to prevent accumulation of water behind the wall. As a minimum,
provide weep holes for drainage. Cover backfill of soil types 2 and 3
(Figure 16) with a surface layer of impervious soil.

Section 4. DESIGN OF FLEXIBLE WALLS

1. ANCHORED BULKHEADS. Anchored bulkheads are formed of flexible sheeting
restrained by tieback and by penetration of sheeting below dredge line. See
Figure 18 for design procedures for three common penetration conditions.

a. Wall Pressures. Compute active and passive pressures using the
appropriate Figures 2 through 7. Determine required depth of penetration of
sheeting and anchor pull from these pressures. See Figure 18 for guidance.

b. Wall Movements. Active pressures are redistributed on the wall by
deflection, moving away from the position of maximum moment. Reduce the
computed maximum moment to allow for flexibility of sheeting. Moment
reduction is a function of the wall flexibility number. See Figure 19
(Reference 10, Anchored Sheet Pile Walls, by Rowe). Select sheeting size by
successive approximations so that sheeting stiffness is compatible with
reduced design moment.

c. Drainage. Include the effect of probable maximum differential head
in computing wall pressures. Where practicable, provide weep holes or
special drainage at a level above mean water to limit differential water
pressures.

7.2-85

7.2-86

d. Anchorage System. Most of the difficulties with anchored bulkheads
are caused by their anchorage. A tieback may be carried to a buried deadman
anchorage, to pile anchorage, parallel wall anchorage, or it may be a
drilled and grouted anchor (see DM-7.3, Chapter 3). See Figure 20 for
criteria for design of deadman anchorage. If a deadman must be positioned
close to a wall, anchorage resistance is decreased and an additional passive
reaction is required for stability at the wall base. Protect tie rods by
wrapping, painting, or encasement to resist corrosion. Where backfill will
settle significantly or unevenly, to avoid loading by overburden, enclose
tie rod in a rigid tube, providing vertical support if needed to eliminate
sag.

e. Example of Computation. See Figure 21 for example of analysis of
anchored bulkhead.

f. Construction Precautions. Precautions during construction are as
follows:

(1) Removal of soft material, or placement of fill in the "passive"
zone should precede the driving of sheet piles.

(2) Deposit backfill by working away from the wall rather than
toward it to avoid trapping, a soft material adjacent to sheeting.

(3) Before anchorage is placed, sheeting is loaded as a cantilever
wall, and safety during construction stages should be checked.

g. Sand Dike Backfill. When granular backfill is scarce, a sand dike
may be place to form a plug across the potential failure surface of the
active wedge as shown in Figure 22. Where such a dike rests on firm
foundation soil, the lateral pressure on the bulkhead will be only the
active pressure of the dike material. For further guidance, see Reference
11, Foundations, Retaining and Earth Structures, by Tschebotarioff.

2. CANTILEVER SHEET PILE WALLS. A cantilever wall derives support from the
passive resistance below the dredge line to support the active pressure from
the soil above the dredge line without an anchorage. This type of wall is
suitable only for heights up to about 15 feet and can be used only in
granular soils or stiff clays. See Figure 23 for a method of analysis
(after Reference 12, Steel Sheet Piling Design Manual, by U.S. Steel
Corporation). For cohesive soils consider no negative pressure in tension
zone. Figures 24 and 25 (Reference 12) may be used for simple cases.

3. INTERNALLY BRACED FLEXIBLE WALLS. To restrain foundation or trench
excavations, flexible walls can be braced laterally as the excavation
proceeds. This restrains lateral movement of the soil and cause loads on
the braces which exceed those expected from active earth pressure. Braces
may be either long raking braces or relatively short horizontal cross
braces between trench walls. Design earth pressure diagram for internally
braced flexible walls are shown in Figure 26 (after Reference 6) for
excavations in sand, soft clay, or stiff clay.

7.2-90

7.2-91

7.2-92

7.2-94

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),
*

4. Take moments about point F. If sum of moments is other than zero

readjust D and repeat calculations until sum of moments around F is

zero.

5. Compute maximum moment at point of zero shear.

6. Increase D by 20% - 40% to result in approximate factory of safety of

1.5 to 2.

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

FIGURE 23 (continued)
Analysis for Cantilever Wall

7.2-96

7.2-99

a. Wall with Raking Braces. When substantial excavation is made before
placing an upper brace, movement of the wall is greatest at the top and
pressures approach active values. See Figure 27 for design criteria.

b. Braced Narrow Cuts. When a narrow cut is braced stiffly as
excavation proceeds, sheeting is restrained at the top and the wall
deflects inward at the base. Design the wall employing the following steps:

(1) Compute factor of safety against bottom instability (Figure
28).

(2) Compute strut forces utilizing the method in upper panel of
Figure 27.

(3) Compute required section for wall and wale using method in
upper panel of Figure 27. In computing the required wall sections, arching
could be accounted for by reducing these pressures somewhat in all but the
upper span. A reduction of 80% of the values shown would be appropriate.

(4) Re-compute strut forces and the required sections of wales and
wall using the pressure diagram of lower panel of Figure 27 for each
construction stage.

(5) Compare strut forces, and required sections computed in Step
(4) to those computed in Step (3) and select the larger force or section for
design. See example in Figure 31.

4. TIED BACK FLEXIBLE WALL. Depending on the width of excavation and
other factors (see Chapter 1) it may be economical to restrain excavation
walls by tie backs. The use of tie backs depends on the existance of
subsoils adequate to provide required anchorage. For multi-level tie back
systems, drilled in tie backs (i.e. anchors) are usually used. For a
single level tie back (e.g., bulkheads), a deadman anchorage, batter pile
anchorage or a parallel wall anchorage are usually considered. For details
on the drilled anchors - process and hardware, see Reference 6. For details
on other anchorage systems see Reference 12 and Reference 13, Foundation
Construction, by Carson.

a. Pressure Distribution. For soft to medium clay use a triangular
distribution, increasing linearly with depth. For all other soils use a
uniform pressure distribution. See Figure 29.

b. Design Procedures. Apply a design procedure similar to internally
braced excavation as shown in Figure 27.

5. EXAMPLE OF COMPUTATION. See Figure 30 for example of analysis of braced
wall of narrow cut, and Figure 31 for an example of excavation in stages.

6. STABILIZING BERMS. On occasion it is practical to increase the
resistance of flexible walls by using stabilizing berms. The lateral
resistance of a stabilizing berm will be less than that for an earth mass
bounded by a horizontal plane at the top elevation of the berm.

7.2-101

7.2-102

7.2-105

7.2-106

7.2-110

a. Method of Analysis. Perform wedge force equilibrium for several
trial failure surfaces, and plot corresponding values of horizontal
resistance for each trial failure surface. The minimum value of horizontal
resistance obtained from the curve is the total passive earth pressure
for the berm. An approximate method of analysis is to replace the berm
with an equivalent sloping plane, and assign an appropriate passive pressure
coefficient.

b. Graphic Procedure. A graphic procedure (Culmann Method) for
evaluating the lateral resistance for granular soils is given in Figure 32.

7. SOLDIER PILES. A frequently used internal bracing system consists of
soldier piles with lagging. The passive earth resistance acting on
individual soldier piles may be computed as shown in Figure 33. For
cohesive soils use uniform resistance of 2c neglecting the soil resistance
to a depth of 1.5 times the pile width b from the bottom of the excavation.
For granular soils, determine K

without wall friction and neglect the

soil resistance to a depth equal to b below the bottom of the excavation.
Total resisting force is computed by assuming the pile to have an effective
width of 3b, for all types of soils. This is because the failure in soil
due to individual pile elements is different from that of continuous walls
for which pressure distributions are derived.

8. GABION STRUCTURES. As illustrated in Figure 34, gabions are
compartmented, rectangular containers made of heavily galvanized steel or
polyvinylchloride (PVC) coated wire, filled with stone from 4 to 8 inches in
size, and are used for control of bank erosion and stabilization. When
water quality is in doubt (12<pH<6) or where high concentration of organic
acid may be present, PVC coated gabions are necessary. At the construction
site, the individual gabion units are laced together and filled with stone.

a. Design. Gabions are designed as mass gravity structures (see Figure
15). When designing a vertical face wall it should be battered at an angle
of about 6 deg. to keep the resultant force toward the back of the wall.
The coefficient of friction between the base of a gabion wall and a
cohesionless soil can be taken as tan[phi] for the soil. The angle of wall
friction, [delta] may be taken as 0.9[phi]. Where the retained material is
mostly sand, a filter cloth or granular filter is recommended to prevent any
leaching of the soil. Determine the unit weight of gabions by assuming the
porosity to be 0.3. Specific gravity of common material ranges between 2.2
(sandstone) and 3.0 (basalt). Along all exposed gabion faces the outer
layer of stones should be hand placed to ensure proper alignment, and a neat
compact square appearance.

b. Cohesive Soils. A system of gabion counterforts is recommended when
designing gab on structures to retain clay slopes. They should be used as
headers and should extend from the front of the wall to a point at least one
gabion length beyond the critical slip circle of the bank. Counterforts may
be spaced from 13 feet (very soft clay) to 30 feet (stiff clay). A filter
is also required on the back of the wall so that clay will not clog the free
draining gabions.

7.2-112

9. REINFORCED EARTH. Reinforced earth is a system of tying vertical facing
units into a soil mass with their tensile strips. It consists of four
elements: (1) a soil backfill, (2) tensile reinforcing strips, (3) facing
elements at boundaries, and (4) mechanical connections between
reinforcements and facing elements. The soil backfill is generally granular
material with not more than 15% by weight passing a No. 200 mesh sieve. It
should not contain materials corrosive to reinforcing strips. Reinforcing
strips include smooth and rough strips of non-corrodable metals or treated
metals about 3 inches wide. Facing consists of steel skin or precast
concrete panels about 7 inches thick.

A wall constructed of reinforced earth is a gravity wall and its safety
should be checked as in Figure 15.

Internal safety of reinforced earth is checked as illustrated in Figure 35.
For further guidance on reinforced earth see Reference 14, Reinforced Earth
Retaining Walls, by Lee, et al. and Reference 15, Symposium of Earth
Reinforcement, Proceedings of a Symposium, by American Society of Civil
Engineers.

10. EARTH FILLED CRIB WALLS. See Figure 36 (Reference 16, Concrete Crib
Retaining Walls, by Portland Cement Association) for types and design
criteria. For stability against external forces, a crib wall is equivalent
to gravity retaining wall (Figure 15). For design of structural elements,
see Reference 17, Foundations, Design and Practice, by Seelye.

Section 5. COFFERDAMS

1. TYPES. Double-wall or cellular cofferdams consist of a line of circular
cells connected by smaller arcs, parallel semi-circular walls connected by
straight diaphragms, or a succession of cloverleaf cells (see Figure 37).
For analysis, these configurations are transformed into equivalent parallel
wall cofferdams of width B.

2. ANALYSIS. Stability depends on ratio of width to height, the resistance
of an inboard berm, if any, and type and drainage of cell fill materials.

a. Exterior Pressures. Usually active and passive pressures act on
exterior faces of the sheeting. However, there are exceptions to this and
these are illustrated in Figure 37.

b. Stability Requirements. A cell must be stable against sliding on
its base, shear failure between sheeting and cell fill, shear failure on
centerline of cell, and it must resist bursting pressures through interlock
tension. These factors are influenced by foundation type. See Figure 37
for design criteria for cofferdams with and without berms, on foundation of
rock or of coarse-grained or fine-grained soil. See Reference 18, Design,
Construction and Performance of Cellular Cofferdams, by Lacroix, et al., for
further guidance.

7.2-116

7.2-118

7.2-121

7.2-124

(1) Sand Base. For cell walls on sand, penetration of sheeting
must be sufficient to avoid piping at interior toe of wall and to prevent
pullout of outboard sheeting.

(2) Clay Base. For cofferdams on clay, penetration of outboard
sheeting usually is controlled by the pullout requirement and piping is not
critical.

(3) Bearing Capacity. For cofferdams on either clay or sand, check
the bearing capacity at the inboard toe by methods of Chapter 4.

c. Cell Deformations. The maximum bulging of cells occurs at about 1/4
of the height above the base of the cofferdam and the cells tilt about 0.02
to 0.03 radians due to the difference in lateral loads on the outboard and
inboard faces. Deflections under the lateral overturning loads are a
function of the dimensions, the foundation support, and the properties of
the cell fill (see Reference 19, Field Study of Cellular Cofferdams, by
Brown).

3. CELL FILL. Clean, coarse-grained, free-draining soils are preferred for
cell fill. They may be placed hydraulically or dumped through water without
compaction or special drainage.

a. Materials. Clean granular fill materials should be used in large
and critical cells. Every alternative should be studied before accepting
fine-grained backfill. These soils produce high bursting pressures and
minimum cell rigidity. Their use may necessitate interior berms, increased
cell width, or possibly consolidation by sand drains or pumping within the
cell. All soft material trapped within the cells must be removed before
filling.

b. Drainage. Weep holes should be installed on inboard sheeting to the
cell fill. For critical cells and marginal fill material, supplementary
drainage by wellpoints, or wells within cells have been used to increase
cell stability.

c. Retardation of Corrosion. When cofferdams are used as permanent
structures, (especially in brackish or seawater, severe corrosion occurs
from top of the the splash zone to a point just below mean low water level.
use Protective coating, corrosion resistant steel and/or cathodic protection
in these areas.

7.2-125

REFERENCES

1. Canadian Geotechnical Society, Excavations and Retaining Structures,
Canadian Foundation Engineering Manual, Part 4, 1978.

2. Caquot, A., and Kerisel, F., Tables for the Calculation of Passive
Pressure, Active Pressure and Bearing Capacity of Foundations,
Gauthier-Villars, Paris.

3. Gray, H., Contribution to the Analysis of Seepage Effects in Backfills,
Geotechnique, 1958.

4. Richart, F.E., and Schmertmann, F., The Effects of Seepage on the
Stability of Sea Walls, Proceedings, First Conference on Coastal
Engineering, University of Florida, Gainesville, FL.

5. Based on work by Terzaghi, K., Anchored Bulkheads, Transaction, ASCE,
Paper No. 2720, Vol. 119, 1954.

6. Goldberg, D.T., Jaworski, W.E., and Gordon, M.D., Lateral Support
Systems and Underpinning, Vol. I, Design and Construction (Summary),
FHWA-RD-75, Federal Highway Administration, 1976.

7. Ingold, T.S., Retaining Wall Performance During Backfilling, Journal
of the Geotechnical Engineering Division, ASCE, Vol. 105, GT5, 1979.

8. Seed, H.B. and Whitman, R.V., Design of Earth Retaining Structures for
Dynamic Loads, Lateral Stresses in the Ground and Design of Earth
Retaining structures, ASCE, Cornell University, 1970.

9. Terzaghi, K., and Peck, R.B., Soil Mechanics in Engineering Practice,
John Wiley & Sons, Inc., New York, 1967.

10. Rowe, P.W., Anchored Sheet Pile Walls, Proceedings, Institution of
Civil Engineers, London, January, 1952.

11. Tschebotarioff, G.P., Foundations, Retaining and Earth Structures, 2nd
Edition, McGraw-Hill, New York, 1973.

12. United States Steel Corporation, Steel Sheet Piling Design Manual,
United States Steel, Pittsburgh, PA., 1975.

13. Carson, A.C., Foundation Construction, McGraw-Hill Book Co., 1965.

14. Lee, K.L., Dean, B. and Vageron, J.M.J., Reinforced Earth Retaining
Walls, Journal of Soil Mechanics and Foundation Division, ASCE, Vol.
99, No. SM10, 1973.

15. ASCE Proceedings, Symposium on Earth Reinforcement, ASCE Annual
Convention, Pittsburg, PA., 1978.

16. Portland Cement Association, Concrete Crib Retaining Walls, Concrete
Information No. St. 46, Chicago, IL., May, 1952.

7.2-126

17. Seelye, E.E., Foundations, Design and Practice, John Wiley & Sons,
Inc., New York, New York, 1956.

18. Lacroix, Y., Esrig, M.I. and Luschem, U., Design, Construction and
Performance of Cellular Cofferdams, Lateral Stresses in the Ground and
Design of Earth Retaining Structures, ASCE, Cornell University, 1970.

19. Brown, P.P., Discussion of Paper by White, Chency and Duke, Field
Study of Cellular Cofferdams, Transaction, ASCE, paper No. 3426, Vol.
128, Part 1, 1963.

20. Naval Facilities Engineering Command

Design Manuals (DM)
DM-2 Series on Structural Engineering
DM-25.04 Seawalls, Bulkheads, and Quaywalls

Copies of Guide Specifications and Design Manuals may be obtained from
the U.S. Naval Publications and Forms Center, 5801 Tabor Avenue,
Philadelphia, PA 19120.

7.2-127 Change 1, September 1986

CHAPTER 4. SHALLOW FOUNDATIONS

Section 1. INTRODUCTION

1. SCOPE. This chapter presents criteria for the design of shallow
foundations, methods of determining allowable bearing pressures, and
treatment of problems in swelling and collapsing subsoils. For the majority
of structures the design of footings is controlled by limiting settlements.
(See RELATED CRITERIA below.) This chapter discusses permissible bearing
pressures as limited by shear failure. Shallow foundations are of the
following types; spread footings for isolated columns, combined footings for
supporting the load from more than one structural unit, strip footings for
walls, and mats or rafts beneath the entire building area. Also, included
is guidance for footings subjected to uplift. Design of deep anchors for
such footings is covered in DM-7.03, Chapter 3.

2. RELATED CRITERIA. See DM-7.01, Chapter 5 for determination of
settlements of shallow foundations. See NAVFAC DM-2.02 for criteria for
loads applied to foundations by various structures and structural design of
foundations.

3. APPLICATIONS. Shallow foundations can be used where there is a suitable
bearing stratum near the surface, no highly compressible layers below, and
calculated settlements are acceptable. Where the bearing stratum at ground
surface is underlain by weaker and more compressible materials, consider the
use of deep foundations or piles. See Chapter 5.

Section 2. BEARING CAPACITY ANALYSIS

1. LIMITATIONS. Allowable bearing pressures for shallow foundations are
limited by two considerations. The safety factor against ultimate shear
failure must be adequate, and settlements under allowable bearing pressure
should not exceed tolerable values. In most cases, settlement governs the
foundation pressures. See DM-7.01, Chapter 5 for evaluation of settlements.
For major structures, where relatively high foundation bearing pressures
yield substantial economy, determine ultimate bearing capacity by detailed
exploration, laboratory testing, and theoretical analysis. For small or
temporary structures, estimate allowable bearing pressures from penetration
tests, performance of nearby buildings, and presumptive bearing values; see
Paragraphs 3 and 4.

2. THEORETICAL BEARING CAPACITY.

a. Ultimate Bearing Capacity. To analyze ultimate bearing capacity for
various loading situations, see Figures 1 through 5. For these analyses the
depth of foundation embedment is assumed to be less than the foundation
width, and friction and adhesion on the foundation's vertical sides are
neglected. In general, the analyses assume a rough footing base such as
would occur with cast-in-place concrete.

7.2-129 Change 1, September 1986

Figures 1 through 5 present ultimate bearing capacity diagrams for
the following cases:

(1) See Figure 1 (Reference 1, Influence of Roughness of Base and
Ground Water Condition-on the Ultimate Bearing Capacity of Foundations, by
Meyerhof) for shallow footings with concentric vertical load. Formulas
shown assume groundwater at a depth below base of footing equal to or
greater than the narrow dimension of the footing.

(2) Use Figure 2 (Reference 1) to determine groundwater effect on
ultimate bearing capacity and the depth of failure zone. For cohesive
soils, changes in groundwater level do not affect theoretical ultimate
bearing capacity.

(3) Use Figure 3a (Reference 2, The Bearing Capacity of Foundations
Under Eccentric and Inclined Loads, by Meyerhof) for inclined load on
continuous horizontal footing and for inclined load on continuous inclined
footing.

(4) Use Figure 3b for eccentric load on horizontal footing.

(5) Use Figures 4a; 4b (Reference 3, The Ultimate Bearing Capacity
of Foundations on Slopes, by Meyerhof) for shallow footing with concentric
vertical load placed on a slope or near top of slope.

(6) Use Figure 5 (Reference 4, The Bearing Capacity of Footings on
a Two-Layer Cohesive Subsoil, by Button) for shallow footing with concentric
vertical load on two layered cohesive soil.

These diagrams assume general shear failure which normally occurs in
dense and relatively incompressible soils. This type of failure is usually
sudden and catastrophic; it is characterized by the existence of a
well-defined failure pattern. In contrast, in loose or relatively
compressible soils, punching or local shear failures may occur at lower
bearing pressures. Punching or local shear failures are characterized by a
poorly defined failure surface, significant vertical compression below the
footing and very little disturbance around the footing perimeter.

To approximate the local or punching shear failures, the bearing
capacity factors should be calculated with reduced strength characteristics
c* and [phi]* defined as:

c* - 0.67 c
[phi]* = tan

(0.67 tan [phi])

For more detailed and precise analysis, see Reference 5, Bearing Capacity of
Shallow Foundations, by Vesic.

b. Allowable Bearing Capacity. To obtain allowable bearing capacity,
use a safety factor of 3 for dead load plus maximum live load. When part of
the live loads are temporary (earthquake, wind, snow, etc.) use a safety
factor of 2. Include in design dead load the effective weight of footing and
soil directly above footing. See Figures 6 and 7 for examples of allowable
bearing capacity calculations.

Change 1, September 1986 7.2-130

7.2-134

7.2-137

7.2-138

c. Soil Strength Parameters.

(1) Cohesive Soils. In the case of fine-grained soils which have
low permeability, total stress strength parameters are used. Value of
cohesion may be determined from laboratory unconfined compression tests,
vane shear tests, or undrained triaxial tests. Shear strength correlations
with standard penetration tests and cone penetration tests may also be used.
(See DM-7.1, Chapter 1.)

(2) Granular Soils. In the case of coarse-grained soils which drain
freely use the effective stress strength parameter ([phi]'). Field tests
(e.g., standard penetration tests or cone penetration) are almost always
used to estimate this strength.

(3) In the case where partial drainage may occur during
construction (e.g., newly compacted fill) perform two analyses, one assuming
drained, the other assuming undrained conditions, and design for the most
conservative results.

3. PRESUMPTIVE BEARING PRESSURES. For preliminary estimates or when
elaborate investigation of soil properties is not justified, use bearing
pressure from Table 1.

a. Utilization. These load intensities are intended to provide a
reasonable safety factor against ultimate failure and to avoid detrimental
settlements of individual footings. Where differential settlements cannot
be tolerated, exploration, testing and analysis should be performed.
Presumptive bearing pressures must be used with caution and verified, if
practicable, by performance of nearby structures.

b. Modifications of Presumptive Bearing Pressures. See Table 2 for
variations in allowable bearing pressure depending on footing size and
position. (See Reference 6, Foundation Analysis and Design, by Bowles for
more detailed analyses of uplift resistance than shown in Table 2). Nominal
bearing pressures may be unreliable for foundations on very soft to
medium-stiff fine-grained soils or over a shallow groundwater table and
should be checked by an estimate of theoretical bearing capacity. Where
bearing strata are underlain by weaker and more compressible material, or
where compressibility of subsoils is constant with depth, analyze
consolidation settlement of the entire foundation (see DM-7.1, Chapter 5).

4. EMPIRICAL, ALLOWABLE BEARING PRESSURES. Allowable bearing pressures for
foundation May be based upon the results of field tests such as the Standard
Penetration Test (SPT) or Cone Penetration Test (CPT). These bearing
pressures are based on maximum foundation settlements, but do not consider
settlement effects due to the adjacent foundations. In the case of closely
spaced foundations where the pressure beneath a footing is influenced by
adjoining footings a detailed settlement analysis must be made.

7.2-141

TABLE 1
Presumptive Values of Allowable Bearing Pressures for Spread
Foundations

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

Allowable Bearing

Pressure

Tons Per sq ft

*)))))))))))))))))))))))1

Type of Bearing Material

Consistency

Recommended

In Place

Value for

Range Use

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Massive crystalline igneous and

Hard, sound rock

60 to 100 80.0

metamorphic rock: granite, dio-

rite, basalt, gneiss, thoroughly

cemented conglomerate (sound

condition allows minor cracks).

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Foliated metamorphic rock:

Medium hard sound

30 to 40 35.0

slate, schist (sound condition

rock

allows minor cracks).

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Sedimentary rock; hard cemented

Medium hard sound

15 to 25 20.0

shales, siltstone, sandstone,

rock

limestone without cavities.

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Weathered or broken bed rock of

Soft rock

8 to 12 10.0

any kind except highly argil-

laceous rock (shale). RQD less

than 25.

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Compaction shale or other highly

Soft rock

8 to 12 10.0

argillaceous rock in sound

condition.

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Well graded mixture of fine and

Very compact

8 to 12 10.0

coarse-grained soil: glacial

till, hardpan, boulder clay

(GW-GC, GC, SC)

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Gravel, gravel-sand mixtures,

Very compact

6 to 10 7.0

boulder gravel mixtures (SW, SP,

Medium to compact

4 to 7 5.0

SW, SP)

Loose

2 to 6 3.0

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Coarse to medium sand, sand with

Very compact

4 to 6 4.0

little gravel (SW, SP)

Medium to compact

2 to 4 3.0

Loose

1 to 3 1.5

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Fine to medium sand, silty or

Very compact

3 to 5 3.0

clayey medium to coarse sand

Medium to compact

2 to 4 2.5

(SW, SM, SC)

Loose

1 to 2 1.5

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-142

TABLE 1 (continued)
Presumptive Values of Allowable Bearing Pressures for Spread
Foundations

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

Allowable Bearing

Pressure

Tons Per sq ft.

*)))))))))))))))))))))))1

Type of Bearing Material

Consistency

Recommended

In Place

Value for

Range Use

*)))))))))))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))1

Homogeneous inorganic clay,

Very stiff to hard

3 to 6 4.0

sandy or silty clay (CL, CH)

Medium to stiff

1 to 3 2.0

Soft

.5 to 1 0.5

Inorganic silt, sandy or clayey

Very stiff to hard

2 to 4 3.0

silt, varved silt-clay-fine Sand

medium to stiff

1 to 3 1.5

Soft

.5 to 1 0.5

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

Notes:

1. Variations of allowable bearing pressure for size, depth and arrangement
of footings are given in Table 2.

2. Compacted fill, placed with control of moisture, density, and lift
thickness, has allowable bearing pressure of equivalent natural soil.

3. Allowable bearing pressure on compressible fine grained soils is
generally limited by considerations of overall settlement of structure.

4. Allowable bearing pressure on organic soils or uncompacted fills is
determined by investigation of individual case.

5. If tabulated recommended value for rock exceeds unconfined compressive
strength of intact specimen, allowable pressures equals unconfined
compressive strength.

7.2-143

TABLE 2
Selection of Allowable Bearing Pressures for Spread Foundations

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

1. For preliminary analysis or in the absence of strength tests of foundation

soil, design and proportion shallow foundations to distribute their

loads using presumptive values of allowable bearing pressure given in

Table 1. Modify the nominal value of allowable bearing pressure for

special conditions in accordance with the following items.

2. The maximum bearing pressure beneath the footing produced by eccentric

loads that include dead plus normal live load plus permanent lateral

loads, shall not exceed the nominal bearing pressure of Table 1.

3. Bearing pressures up to one-third in excess of the nominal bearing

values are permitted for transient live load from wind or earthquake.

If overload from wind or earthquake exceeds one-third of nominal bearing

pressures, increase allowable bearing pressures by one-third of nominal

value.

4. Extend footings on soft rock or on any soil to a minimum depth of 18

inches below adjacent ground surface or surface of adjacent floor bearing

on soil, whichever elevation is the lowest.

5. For footings on soft rock or on coarse-grained soil, increase allowable

bearing pressures by 5 percent of the nominal values for each foot of

depth below the minimum depth specified in 4.

6. Apply the nominal bearing pressures of the three categories of hard or

medium hard rock shown on Table 1 where base of foundation lies on rock

surface. Where the foundation extends below the rock surface increase

the allowable bearing pressure by 10 percent of the nominal values for

each additional foot of depth extending below the surface.

7. For footing smaller than 3 feet in least lateral dimension, the allowable

bearing pressure shall be one-third of the nominal bearing pressure

multiplied by the least lateral dimension in feet.

8. Where the bearing stratum is underlain by a weaker material determine

the allowable bearing pressure as follows:

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-144

a. Standard Penetration Test. Relationships are presented in Reference
7, Foundation Engineering, by Peck, Hanson and Thornburn, for allowable
bearing values in terms of standard penetration resistance and for limiting
settlement. When SPT tests are available, use the correlation in DM-7.1,
Chapter 2 to determine relative density and Figure 6, DM-7.1, Chapter 3 to
estimate [phi] values. Use Figure 1 to compute ultimate bearing pressure.

b. Cone Penetration Test. The results of CPT may be used directly to
compute allowable bearing pressure for coarse-grained soils. See Figure 8
(Reference 8, Shallow Foundations, by the Canadian Geotechnical Society).

c. Bearing Capacity From Pressuremeter. If pressuremeter is used to
determine in situ soil characteristics, bearing capacity can be computed
from these test results. (See Reference 8.)

Section 3. SPREAD FOOTING DESIGN CONSIDERATIONS

1. FOUNDATION DEPTH. In general footings should be carried below:

(a) The depth of frost penetration;

(b) Zones of high volume change due to moisture fluctuations;

(d) Disturbed upper soils;

(e) Uncontrolled fills;

(f) Scour depths in rivers and streams.

(g) Zones of collapse-susceptible soils.

2. ALTERNATIVE FOUNDATION METHODS - Light Structures. Light structures may
be supported by other types of shallow foundation treatment such as: (a)
deep perimeter wall footings; (b) overexcavation and compaction in footing
lines; (c) mat design with thickened edge; (d) preloading surcharge.

3. PROPORTIONING INDIVIDUAL FOOTINGS. Where significant compression will
not occur in strata below a depth equal to the distance between footings,
individual footings should be proportioned to give equal settlements, using
formulas from DM-7.1, Chapter 5. See Figure 9 for an example.

4. CORROSION PROTECTION. Foundation design should consider potentially
detrimental substances in soils, such as chlorides and sulphates, with
appropriate protection for reinforcement, concrete and metal piping. If the
analysis indicates sulphate concentration to be more than 0.5% in the soil
or more than 1200 parts per million in the groundwater, the use of a
sulphate resisting cement such as Type V Portland cement should be
considered. In additions, other protection such as lower water-cement
ratio, bituminous coating, etc. may be required depending upon the sulphate
concentration. See Reference 9, Sulphates in soils and Groundwaters, BRS
Digest, for guidance.

7.2-146

7.2-147

7.2-149

Electrical corrosive properties of soil are important where metal
structures such as pipe lines, etc. are buried underground. A resistivity
survey of the site may be necessary to evaluate the need for cathodic
protection.

Section 4. MAT AND CONTINUOUS BEAM FOUNDATIONS

1. APPLICATIONS. Depending on economic considerations mat foundations are
generally appropriate if the sum of individual footing base areas exceeds
about one-half the total foundation area; if the subsurface strata contain
cavities or compressible lenses; if shallow shear strain settlements
predominate and the mat would equalize differential settlements; or if
resistance to hydrostatic uplift is required.

2. STABILITY AND SETTLEMENT REQUIREMENTS. As with other types of
foundations, a mat foundation must have an ample factor of safety (see
Section 2) against overall shear failure and it must not exhibit intolerable
settlement (see DM-7.1, Chapter 5).

Since mat footings are simply large footings, the bearing capacity
principles outlined in Sections 2 and 3 of this chapter are applicable. The
ultimate bearing capacity of large mats on coarse-grained soils is usually
very high and design is usually controlled by settlement (see DM-7.1,
Chapter 5). For mats on cohesive soils, shear strength parameters for soils
at depth must be determined for the proper evaluation of factor of safety
against deepseated failure.

3. DESIGN PROCEDURES. A design method based on the theory for beams or
plates on discreet elastic foundations (Reference 10, Beams on Elastic
Foundation, by Hetenyi) has been recommended by ACI Committee 436 (Reference
11, Suggested Design Procedures for Combined Footings Mats) for design ofmat
foundations. This analysis is suitable for foundations on
coarse-grained soils.

a. Two-dimensional Problems. For walls or crane track footings or mat
foundations subjected to plane strain, such as drydock walls and linear
blocking loads, use the procedures of Table 3 and Figures 10 and 11
(Reference 10). Superpose shear, moment, and deflection produced by
separate loads to obtain the effect of combined loads.

b. Three-dimensional Problems. For individual loads applied in
irregular pattern to a roughly equi-dimensional mat, analyze stresses by
methods of plates on elastic foundations. Use the procedures of Table 4 and
Figure 12.

Superpose shear, moment, or deflection produced by separate loads to
obtain the effect of combined loads.

7.2-150

7.2-151

7.2-152

[retrieve TABLE 4: (continued) Definitions and Procedures, Mats on Elastic
Foundations]

7.2-156

c. Modulus of Subgrade Reaction. The modulus of subgrade reaction (K)
is expressed as:

K= p/[W-DELTA]H

where: p = contact pressure (stress unit)
[W-DELTA] = soil deformation (length)

(1) K varies with the width and shape of the loaded area.
Empirical correction for strip footings from Reference 12, Evaluation of
Coefficient of Subgrade Reaction, by Terzaghi are:

(a) Cohesive soil.

= K

, /

where: K

= coefficient of subgrade reaction for foundation of width b

= coefficient of subgrade reaction for a 1' x 1' plate

If the loaded area is of width, b, and length, m

, k

assumes the value:

m + 0.5

)))))

(

)))))))

)

b 1.5m

If actual plate load tests on cohesive soil are not available, estimates of
K

can be made in general accordance with the recommendations in Reference

12. If actual plate load tests are not available use correlation for K

in Figure 6, DM-7.1, Chapter 5.

(b) Granular soil.
b + 1
K

= K

(

)))))

)

as determined from

extrapolation of plate bearing tests should be utilized with judgement and
care. Unlike the deformation in full size mat the deformation from plate
load tests is not reflective of the underlying deeper strata. Also results
from plate load tests on saturated or partially saturated clays may be
unreliable because time may not permit complete consolidation of loaded
clay.

(2) An estimate of K

may be obtained by back calculating from a

settlement analysis. The settlement of the mat can be calculated assuming a
uniform contact pressure and utilizing the methods outlined in DM-7.1,
Chapter 4 5. The contact pressure is then divided by the average settlement
to obtain an estimate of K

P
K

)))))))))))))))

[W-DELTA]H

avg

where [W-DELTA]H

avg

= average computed settlement of the mat.

7.2-158

For a flexible circular mat resting on a perfectly elastic material
[W-DELTA]H

avg

0.85 x settlement at the center. For other shapes see

DM-7.1, Chapter 5, Table 1.

d. Numerical Methods. Methods of analyses of mat foundation which
account for the stiffness of the superstructure and the foundation, in which
the soil is modelled as an elastic half space continuum utilizing finite
element techniques are more accurate. A variety of soil constitutive
relationships such as linear elastic, non-linear elastic, elasto-plastic,
etc. can be utilized. Finite element techniques are well suited to these
problems. See Appendix for listing of computer programs.

Section 5. FOUNDATIONS ON ENGINEERED FILL

1. UTILIZATION. Fills placed with controlled compaction may be used
beneath structures for the following purposes:

(a) To raise the general grade of the structure or to replace
unsuitable foundation soils.

(b) To provide a relatively stiff mat over soft subsoils in order to
spread bearing pressures from column loads and decrease column settlements.

(d) To accelerate subsoil consolidation and to eliminate all or part of
settlement of the completed structure when used with surcharge.

2. COMPACTION CONTROL. Rigidity, strength, and homogeneity of many natural
soils may be increased by controlled compaction with appropriate equipment.
A complete discussion of compaction requirements and control is presented in
Chapter 2. Other methods of densifying in-place soils are given in DM-7.3,
Chapter 2.

3. GEOMETRIC LIMITS OF COMPACTION. The limits of the zone of compacted soil
beneath a footing should consider the vertical stresses imposed by the
footing (stress-bulb) on the soils beneath it. Recommended requirements for
compaction beneath a square and a continuous footing are illustrated in
Figure 13. For large footings, the necessary depth of compacted fill should
be determined from a settlement analysis.

Section 6. FOUNDATIONS ON EXPANSIVE SOILS

1. POTENTIAL EXPANSION CONDITIONS. Soils which undergo volume changes upon
wetting and drying are termed expansive or swelling soils. If surface clays
above the water table have a PI greater than about 22 (CH clays) and
relatively low natural water content, potential expansion must be
considered. These soils are most commonly found in arid climates with a
deficiency of rainfall, over-evaporation, and where the groundwater table
is low. Mottled, fractured,

7.2-159

7.2-160

or slickensided clays, showing evidence of past desiccation, are
particularly troublesome. For other causes of swelling in soils and for the
computations of resulting heave see DM-7.1, Chapter 5, and DM-7.3, Chapter 3
for further guidance.

2. ELIMINATING SOIL EXPANSION POTENTIAL. Where economically feasible,
remove potentially expansive soils from beneath footings and replace with
compacted fill of granular soils or nonexpansive materials. If this cannot
be done, consider spread footings or drilled and underreamed caissons
founded below the zone of active swelling. Design the shafts of such
foundations with sufficient reinforcing to resist tensile forces applied to
shaft by friction or adhesion in the swelling materials. Reinforcing must
be carried into the belled section to a point 4" above the base. At any
depth, tensile forces exerted on a shaft equal circumferential area of the
shaft times the difference between average swelling pressure above and below
the point under consideration.

Placing the base of foundation near the water table reduces heave damage
because of little change in moisture content. For construction techniques
in such soil see Figure 14 (top and center, Reference 13, Soil Mechanics
and Foundation, by Parcher and Means), DM-7.3, Chapter 3, and Reference 14,
Design and Performance of Mat Foundation on Expansive Clay, by Lytton and
Woodburn.

Footing foundations can be successful if sufficient dead load is exerted
to eliminate heave completely or reduce it significantly in conjunction with
a structure rigid enough to withstand stress due to heaving. See DM-7.1
Chapter 5, and DM-7.3, Chapter 3 for methods of estimating the magnitude of
swell.

3. MINIMIZING EXPANSION EFFECTS. Where it is not economically leasible to
remove expansive materials or to support foundations below depths of
possible expansion, the effects can be minimized as follows:

(a) Where large seasonal changes in soil moisture are responsible for
swelling, schedule construction during or immediately after a prolonged
rainy period when there will be less potential volume change in the future.

(b) For concrete floor slabs placed directly on potentially expansive
clays, provide expansion joints so the floor can move freely from the
structural frame.

(c) For foundations on fill materials containing plastic fines and
susceptible to swelling, place fill at moisture content above optimum with
density no higher than required for strength and rigidity. Excessive
compaction will result in greater swelling.

(d) Grade beams should contain sufficient steel reinforcement to resist
the horizontal and vertical thrust of swelling soils. If practical, place
compressible joint filler or open blocks or boxes beneath grade beams to
minimize swelling pressures.

(e) Provide impervious blankets and surface grading around the
foundations to prevent infiltration of surface water.

7.2-161

(f) Locate water and drainage lines so that if any leakage occurs,
water will not be readily accessible to foundation soils thereby causing
damage.

(g) Consider stabilization of the foundation soils and backfill mate
materials by lime and other agents.

For further guidance see Reference 15, Foundations on Expansive Soils,
by Chen, and DM-7.3, Chapter 3.

4. COLLAPSING SOILS. Many collapsing soils will slake upon immersion, but
this is not a definitive indicator. Definite identification requires a pair
of consolidation tests with and without saturation, or by plate load tests
where water is added with the plate under stress. In the case of
collapsible soil, the e-log p curve for the specimen, which was allowed to
come in contact with water, is below that of the dry specimen. See DM-7.1,
Chapter 3 for testing procedures.

(a) If positive measures are practical for avoiding water foundation
contact, the "dry" strength of soil can be used for design purposes.

(b) Alternately, under some conditions, prewetting of the soil is found
effective in reducing settlements. By this process, the soil structure
breaks down resulting in its densification. This increases its strength
and reduces the total and differential settlement. This method is not very
successful especially where little additional load is applied during
wetting. For further guidance see DM-7.3, Chapter 3, and Reference 7.

Section 7. FOUNDATION WATERPROOFING

1. APPLICATIONS. See Table 5 for general requirements for waterproofing,
dampproofing, and waterstops. See References 16, 17, and 18; Foundation
Design, by Teng, NAVFAC TS-07110, Membrane Waterproofing, and NAVFAC
TS-07160, Bituminous Dampproofing, respectively, for guidance. For
basements below ground, two general schemes are employed as follows:

(a) Where the permanent water table is above the top of basement slab,
provide pressure resistant slab (pressure slab) or relieve uplift pressures
by underdrainage (relieved slab).

(b) Where the water table is deep but infiltration of surface water
dampens backfill surrounding basement, provide dampproof walls and slabs
(see Table 5, Dampproofing).

2. PRESSURE AND RELIEVED SLABS.

a. Pressure Slabs. In general, the choice between pressure or relieved
slab depends on overall economy, maintenance, layout, and operation, and
must be evaluated individually for each project. For basements extending
only a small depth below groundwater, a pressure slab to resist maximum
probable hydrostatic uplift usually is economical. Also, when the soil
below water level is very pervious, an extensive and consequently very
costly drainage system may be necessary. See Case A, Figure 15. Drainage
material should be

7.2-163

7.2-168

sound, clean gravel or crushed stone graded between 3/4 and 2 inches,
compacted by two or three coverages of vibrating base plate compactor. Open
joint drain pipe should be added beneath slabs of large plan dimensions.
Provide water- stops at the construction joints between pressure slab and
wall.

b. Relieved Slabs. For basements at considerable depth below
groundwater level, it is usually economical to provide pressure relief
beneath the foundation slab. See Cases B and C, Figure 15. If pervious
materials of great depth underlie the foundation level, include a wall drain
and drainage course beneath the slab. See DM-7.1, Chapter 6 for filter
requirements and drain spacing. If foundation walls can be carried
economically to underlying sound impervious rock or thick impervious
stratum, omit wall drains. Arrange sumps for drainage discharge to avoid
aerating drainage course.

3. WATERPROOFING REQUIREMENTS. In addition to leakage under pressure
through joints and cracks, water may move through basement walls and floors
by capillary action and as water vapor. A drainage course can be used to
interrupt capillary action, but it will not prevent movement of water vapor
through slabs. Plastic vapor barriers are useful in providing an effective
vapor barrier.

a. Membrane Waterproofing and Dampproofing. Apply membrane (see Figure
15B) for basements utilized for routine purposes where appearances are
unimportant and some dampness is tolerable.

b. Cement Plaster Waterproofing. Where it is important to prevent
dampness or moisture in a basement, specify cement plaster waterproofing,
consisting of sand-cement mortar hand troweled on chipped and roughened
concrete surface. Properly applied, this is a very effective method
against dampness and moisture.

Section 8. UPLIFT RESISTANCE

1. ROCK FOUNDATION. Resistance to direct uplift of tower legs, guys, and
antennas, where the foundation is resting directly over rock, may be
provided by reinforcing bars grouted in rock. In the absence of pullout
tests, determine uplift resistance by empirical formulas of Figures 16 and
18. These formulas apply to bars in fractured rock near the rock surface.
Higher shear strength is to be expected in sound, unweathered rock. To
develop rock strength, sufficient bond must be provided by grout surrounding
the bar. Bond strengths May be increase by using washers, rock bolts,
deformed bars, or splayed bar ends.

Guidance for design rules is given in DM-7.3, Chapter 3 and quality control
associated with pre-stressed, cement grouted rock anchors is found in
Reference 19, Rock Anchors - State of the Art, by Littlejohn and Bruce.

2. SOIL FOUNDATION. For sustained uplift on a footing, see Table 2.
Transient uplift from live loads applied to footings, piers, posts or
anchors is

7.2-169

7.2-171

analyzed as shown in Figure 17. Tower guy anchorage in soil is analyzed in
Figure 18. For a deadman in weak soil, it may be feasible to replace a
considerable volume of soil with granular backfill and construct the block
within the new backfill. If this is done, the passive wedge should be
contained entirely within the granular fill, and the stresses on the
remaining weak material should be investigated. See Reference 6 for
guidance.

3. CORROSION. For temporary anchors minimal protection is needed unless
the environments are such that rapid deterioration takes place. Permanent
anchor bars are covered with grout. In corrosive environments it is common
practice to provide additional protection by coating with material (epoxy,
polyester resin) with proven resistance to existing or anticipated corrosive
agents. The coating agent should not have any adverse effect on the bond.

4. ROCK AND SOIL ANCHORS. When the load to be resisted is large, wire
tendons which can also be prestressed to reduce movements are employed.

Also, because of corrosion special precautions may be necessary when
permanent anchors are provided in marine environments. In the analysis of
anchors, because of submergence, the bouyant unit weight of soils should be
used. The buildup of excess pore pressure due to repetitive loads should
also be evaluated in the case of granular soils. For a discussion of cyclic
mobility and liquefaction see DM-7.3, Chapter 1. For the design of anchors
see DM-7.3, Chapter 3.

7.2-173

REFERENCES

1. Meyerhof, G.G., Influence of Roughness of Base and Ground Water
Condition on the Ultimate Bearing Capacity of Foundations,
Geotechnique, 1955.

2. Meyerhof, G.G., The Bearing Capacity of Foundations Under Eccentric
and Inclined Loads, Proceedings, Third International Conference on Soil
Mechanics and Foundation Engineering, Zurich, 1953.

3. Meyerhof, G.G., The Ultimate Bearing Capacity of Foundations on Slopes,
Proceedings, Fourth International Conference on Soil Mechanics and
Foundation Engineering, London, 1957.

4. Button, S.F., The Bearing Capacity of Footings on a Two-Layer Cohesive
Subsoil, Proceedings, Third International Conference on Soil Mechanics
and Foundation Engineering, Zurich, 1953.

5. Vesic, A. S. Bearing Capacity of Shallow Foundations, Foundation
Engineering Handbook, Winterkorn and Fang, eds., Van Nostrand Reinhold
Company, New York, Chapter 3, 1975.

6. Bowles, J.E., Foundation Analysis and Design, McGraw Hill Book Co., New
York, pp. 137-139, 1977

7. Peck, R.B., Hanson, W.E. and Thornburn, T.H., Foundation Engineering,
2nd Edition, John Wiley & Sons, Inc., New York, 1974.

8. Canadian Geotechnical Society, Shallow Foundations, Canadian
Foundation Engineering Manual, Montreal, Canada, Part 2, 1978.

9. CP2004, Sulphates in Soils and Groundwaters, Classification and
Recommendations, BRS Digest, No. 90, Second Series, London, England,
1972.

10. Hetenyi, M., Beams on Elastic Foundation, University of Michigan Press,
Ann Arbor, MI, 1946.

11. ACI Committee 436, Suggested Design Procedures for Combined Footings
and Mats, American Concrete Institute, 1966.

12. Terzaghi, K., Evaluation of Coefficient of Subgrade Reaction,
Geotechnique, Vol. 5, No. 4, 1955.

13. Parcher, J.V. and Means, R.E., Soil Mechanics and Foundations, Charles
E. Merril Publishing Company, Columbus, OH, 1968.

14. Lytton, R.L. and Woodburn, J.A., Design and Performance of Mat
Foundations on Expansive Clay, Proceedings of the Third International
Conference on Expansive Soils, 1973.

15. Chen, F.H., Foundations on Expansive Soils, Footing Foundations,
Elsevier Scientific Publishing Co., New York, Chapter 5, 1975.

7.2-174

16. Teng, W.C., Foundation Drainage and Waterproofing, Foundation Design,
Prentice Hall, Englewood Cliffs, NJ, Chapter 5, 1962.

17. NAVFAC TS-07110, Membrane Waterproofing, Naval Facilities Engineering
Command, 1979.

18. NAVFAC TS-07160, Bituminous Dampproofing, Naval Facilities Engineering
Command, 1978.

19. Littlejohn, G.S. and Bruce, D.A., Rock Anchors-State of the Art,
Foundation Publications Ltd., England, 1977.

20. NAVFAC DM-2.02, Loads, Naval Facilities Engineering Command, 1986.

Copies of Guide Specifications and Design Manuals may be obtained from
the U.S. Naval Publications and Forms Center, 5801 Tabor Avenue,
Philadelphia, PA 19120.

7.2-175 Change 1, September 1986

CHAPTER 5. DEEP FOUNDATIONS

Section 1. INTRODUCTION

1. SCOPE. This chapter presents information on the common types of deep
foundations, analysis and design procedures, and installation procedures.
Deep foundations, as used in this chapter, refer to foundations which obtain
support at some depth below the structure, generally with a foundation depth
to width ratio (D/B) exceeding five. These include driven piles, drilled
piles, drilled piers/caissons, and foundations installed in open or braced
excavations well below the general structure. Diaphragm walls are discussed
in DM-7.03, Chapter 3.

2. APPLICATION. Deep foundations are used in a variety of applications
including:

(a) To transmit loads through an upper weak and/or compressible stratum
to underlying competent zone.

(b) To provide support in areas where shallow foundations are
impractical, such as underwater, in close proximity to existing structures,
and other conditions.

3. RELATED CRITERIA. For additional criteria relating to the design of
deep foundations and the selection of driving equipment and apparatus, see
the following sources:

Subject Source

Pile Driving Equipment NAVFAC DM-38.04
General Criteria for Piling in Waterfront Construction NAVFAC DM-25.06

4. LOCAL PRACTICE. The choice of the type of deep foundation such as pile
type(s), pile design capacity, and installation procedures is highly
dependent on local experience and practice. A design engineer unfamiliar
with these local practices should contact local building/engineering
departments, local foundation contractors, and/or local foundation
consultants.

5. INVESTIGATION PROGRAM. Adequate subsurface exploration must precede the
design of pile foundations. Investigations must include the following:

(a) Geological section showing pattern of major strata and presence of
Possible obstructions, such as boulders, buried debris, etc.

(b) Sufficient test data to estimate Strength and compressibility
parameters of major strata.

For field explorations and testing requirements, see DM-7.01, Chapter 2.

7.2-177 Change 1, September 1986

6. CONSTRUCTION INSPECTION. The performance of a deep foundation is highly
dependent on the installation procedures, quality of workmanship, and
installation/design changes made in the field. Thus, inspection of the deep
foundation installation by a geotechnical engineer normally should be
required.

Section 2. FOUNDATION TYPES AND DESIGN CRITERIA

1. COMMON TYPES. Tables 1 and 2 summarize the types of deep foundations,
fabricated from wood, steel, or concrete, in common usage in the United
States. Table 1 presents pile types and Table 2 presents excavated
foundation types including drilled piers/caissons. General comments on
applicability of the various foundation types are given in Table 2, but
local experience and practices, comparative costs, and construction
constraints should be reviewed carefully for each site.

a. Driven Piles. These are piles which are driven into the ground and
include both low displacement and high displacement piles. Low
displacement piles include H and I section steel piles. Open end piles
which do not form a plug, jetted piles, and pre-bored driven piles may
function as low displacement piles. Solid section piles hollow section
closed end piles, and open end piles forming a soil plug function as high
displacement piles. All the pile types in Table 1 except auger-placed piles
are driven piles.

b. Excavated Foundations. These foundations include both drilled piles
and piers and foundations constructed in open or braced excavations (see
Reference 1, Foundation Design, by Teng). Drilled piles include
auger-placed piles and drilled pier/caissons either straight shaft or
belled.

2. OTHER DEEP FOUNDATION TYPES. Tables 1 and 2 include only the most
commonly used pile types and deep foundation construction procedures. New
and innovative types are being developed constantly, and each must be
appraised on its own merits.

a. Drilled-in Tubular Piles. These consist of heavy-gauge steel tubular
pile capable of being rotated into the ground for structure support. Soils
in the tube may be removed and replaced with concrete. Used in penetration
of soil containing boulders and obstructions, or drilling of rock socket to
resist uplift and lateral forces. Steel H-sections within concrete cores
are used to develop full end bearing for high load capacity.

b. TPT (Tapered Pile Tip) Piles. These consist of a mandrel drive
corrugated shell with an enlarged precast concrete base. This type of pile
is usually considered in conditions suitable for pressure injected footings.
The principal claimed advantage is the avoidance of punching through a
relatively thin bearing stratum.

c. Interpiles. These consist of an uncased concrete pile, formed by a
mandrel riven steel plate. A steel pipe mandrel of smaller diameter than
the plate is used, and the void created by the driven plate is kept
continuously filled with concrete. It is claimed that this pile develops
greater side friction in a granular soil than drilled piers and conventional
driven piles.

Change 1, September 1986 7.2-178

TABLE 1
Design Criteria for Bearing Piles

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

PILE TYPE

TIMBER

STEEL - H SECTIONS

*)))))))))))))))*))))))))))))))))))))))))))))))))))*))))))))))))))))))))))))))))))1

CONSIDER FOR

LENGTH OF

30-60FT

40-100 FT

APPLICABLE

ASTM -D25

ASTM-A36

MATERIAL SPEC-

IFICATIONS.

MAXIMUM

MEASURED AT MOST CRITICAL POINT,

12,000 PAI.

STRESSES.

1200 PSI FOR SOUTHERN PINE AND

DOUGLAS FIR. SEE U.S. D.A. WOOD

HANDBOOK NO.72 FOR STRESS VALUES

OF OTHER SPECIES.

CONSIDER FOR

10 - 50 MNS

DESIGN LOADS

40 -120 TONS

DISADVANTAGES

DIFFICULT TO SPLICE.

VULNERABLE TO CORROSION WHERE

VULNERABLE TO DAMAGE IN HARD

EXPOSED HP SECTION MAY BE

DRIVING, TIP MAY HAVE TO BE

DAMAGED OR DEFLECTED BY MAJOR

PROTECTED. VULNERABLE TO DECAY

OBSTRUCTIONS.

UNLESS TREATED, WHEN PILES ARE

INTERMITTENTLY SUBMERGED.

ADVANTAGES

COMPARATIVELY LOW INITIAL COST.

EASY TO SPLICE.

PERMANENTLY SUBMERGED PILES ARE

AVAILABLE IN VARIOUS LENGTHS

RESISTANT TO DECAY,

AND SIZES. HIGH CAPACITY.

EASY TO HANDLE.

SMALL DISPLACEMENT.

ABLE TO PENETRATE THROUGH

LIGHT OBSTRUCTIONS.

HARDER OBSTRUCTIONS MAY BE

PENETRATED WITH APPROPRIATE

POINT PROTECTION OR WHERE

PENETRATION OF SOFT ROCK IS

REQUIRED.

REMARKS

BEST SUITED FOR FRICTION PILE IN

BEST SUITED FOR ENDBEARING ON

GRANULAR MATERIAL.

ROCK. REDUCE ALLOWABLE

CAPACITY FOR CORROSIVE

LOCATIONS.

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-179

TABLE 1 (continued)
Design Criteria for Bearing Piles

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

PRECAST CONCRETE

CAST-IN-PLACE CONCRETE (THIN

PILE TYPE

(INCLUDING PRESTRESSED)

SHELL DRIVEN WITH MANDREL)

*)))))))))))))*))))))))))))))))))))))))))))))))))*))))))))))))))))))))))))))))))))*

CONSIDER FOR

40-50 FT FOR PRECAST

10-120 FT BUT TYPICALLY IN THE

LENGTH OF

60-100 FT FOR PRESTRESSED.

50-90 FT.RANGE

APPLICABLE

ACI 318 FOR CONCRETE

ACI CODE 318-FOR CONCRETE.

MATERAL SPEC-

ASTM A15-FOR REINFORCING STEEL

IFICATIONS,

MAXIMUM

FOR PRECAST-33 % OF 28 DAY

33% OF 28-DAY STRENGTH OF

STRESSES.

STRENGTH OF CONCRETE.

CONCRETE, WITH INCREASE TO 40%

FOR PRESTRESSED- F

=0.33

OF 28 DAY STRENGTH.

-0.27F

PROVIDING:

(WHERE: F

IS THE EFFECTIVE

(A) CASING IS A MINIMUM 14 GAUGE

PRESTRESS STRESS ON THE GROSS

THICKNESS

SECTION).

(B) CASING IS SEAMLESS OR WITH

WELDED SEAMS

STRENGTH TO CONCRETE 28 DAY

STRENGTH IS NOT LESS THAN 6.

(D) PILE DIAMETER IS NOT

GREATER THAN 17".

SPECIFICALLY DESIGNED FOR A WIDE

RANGE OF LOADS.

DISADVANTAGES

UNLESS PRESTRESSED, VULNERABLE TO

DIFFICULT TO SPLICE AFTER

HANDLING RELATIVELY HIGH BREAKAGE

CONCRETING. REDRIVING NOT

RATE ESPECIALLY WHEN PILES ARE TO

RECOMMENDED. THIN SHELL

TO BE SPLICED.

VULNERABLE DURING DRIVING TO

HIGH INITIAL COST.

EXCESSIVE EARTH PRESSURE OR

CONSIDERABLE DISPLACEMENT

IMPACT.

PRESTRESSED DIFFICULT TO SPLICE.

CONSIDERABLE DISPLACEMENT.

ADVANTAGES

HIGH LOAD CAPACITIES.

INITIAL ECONOMY.

CORROSION RESISTANCE CAN BE

TAPERED SECTIONS PROVIDE HIGHER

ATTAINED. HARD DRIVING POSSIBLE.

BEARING RESISTANCE IN GRANULAR

STRATUM CAN BE INTERNALLY

INSPECTED AFTER DRIVING

RELATIVELY LESS WASTE STEEL

MATERIAL. CAN BE DESIGNED AS

END BEARING OR FRICTION PILE,

GENERALLY WADED IN THE

40-100 TON RANGE.

REMARKS

CYLINDER PILES IN PARTICULAR ARE

BEST SUITED FOR MEDIUM LOAD

SUITED FOR BENDING RESISTANCE.

FRICTION PILES IN GRANULAR

GENERAL LOADING RANGE IS 40-400

MATERIALS.

TONS.

.)))))))))))))2))

)))))))))))))))))

)))))))))))))))2)

)))))))))))))))))

))))))))))))))-

7.2-180

TABLE 1 (continued)
Design Criteria for Bearing Piles

+)))))))))))))0))))))))))))))))))))))))))))))))))0)))))))))))))))))))))))))))))))),

CAST-IN-PLACE CONCRETE PILES

PILE TYPE

(SHELLS DRIVEN WITHOUT MANDREL)

PRESSURE INJECTED FOOTINGS

/)))))))))))))3))))))))))))))))))))))))))))))))))3))))))))))))))))))))))))))))))))1

CONSIDER FOR

LENGTH OF

30-80 FT.

10 TO 60 FT

APPLICABLE

ACI CODE 318

MATERIAL

SPECIFI-

CATION

MAXIMUM

33% OF 28 - DAY STRENGTH OF

33% OF 28-DAY STRENGTH OF

STRESSES

CONCRETE 9,000 PSI IN SHELL,

CONCRETE. 9,000 PSI FOR PIPE

THAN 1/8 INCH THICK.

SHELL IF THICKNESS GREATER THAN

1/8 INCH

CONSIDER FOR

50-70 TONS

60-120 TONS.

DESIGN LOADS

BASE OF FOOTING CANNOT BE MADE

DISADVANT-

HARD TO SPLICE AFTER CONCRETING.

IN CLAY OR WHEN HARD SPOTS

AGES

CONSIDERABLE DISPLACEMENT

E.G. ROCK LEDGES) ARE PRESENT

IN SOIL PENETRATED. WHEN CLAY

LAYERS MUST BE PENETRATED TO

REACH SUITABLE MATERAL,

SPECIAL PRECAUTIONS ARE

ADVANTAGES

CAN BE REDRIVEN.

REQUIRED FOR SHAFTS IF IN

GROUPS.

SHELL NOT EASILY DAMAGED.

PROVIDES MEANS OF PLACING HIGH

CAPACITY FOOTINGS ON BEARING

STRATUM WITHOUT NECESSITY FOR

EXCAVATION OR DEWATERING.

HIGH BLOW ENERGY AVAILABLE FOR

OVERCOMING OBSTRUCTIONS.

GREAT UPLIFT RESISTANCE IF

SUITABLY REINFORCED.

REMARKS

BEST SUITED FOR FRICTION PILES OF

BEST SUITED FOR GRANULAR SOILS

MEDIUM LENGTH.

WHERE BEARING IS ACHIEVED

THROUGH COMPACTION AROUND

BASE.

MINIMUM SPACING 4'-6" ON

CENTER.

.)))))))))))))2))))))))))))))))))))))))))))))))))2))))))))))))))))))))))))))))))))-

7.2-181

TABLE 1 (continued)
Design Criteria for Bearing Piles

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

PILE TYPE

CONCRETE FILLED STEEL PIPE PILES

COMPOSITE PILES

*)))))))))))))*))))))))))))))))))))))))))))))))))*))))))))))))))))))))))))))))))))1

CONSIDER FOR

LENGTH OF

40-120 FT OR MORE

60-200 FT

APPLICABLE

ASTM A36-FOR CORE.

ACI CODE 318-FOR CONCRETE

MATERIAL

ASTM A252-FOR PIPE.

ASTM A36-FOR STRUCTURAL SECTION.

SPECIFIC-

ACI CODE 318-FOR CONCRETE.

ASTM A252-FOR STEEL PIPE.

ATIONS

ASTM D25 -FOR TIMBER.

MAXIMUM

9,000 PSI FOR PIPE SHELL

33% OF 28-DAY STRENGTH OF

STRESSES.

33% OF 28-DAY STRENGTH OF CON-

CONCRETE.

CRETE. 12,000 PSI ON STEEL CORES

9,000 PSI FOR STRUCTURAL AND

OF STRUCTURAL REINFORCING STEEL.

PIPE SECTIONS.

SAME AS TIMBER PILES FOR WOOD

COMPOSITE.

CONSIDER FOR

80-120 TONS WITHOUT CORES.

30-100 TONS.

DESIGN WAD

500-1,500 TONS WITH CORES.

DISADVANT-

HIGH INITIAL COST

DIFFICULT TO ATTAIN GOOD JOINT

AGES

DISPLACEMENT FOR CLOSED END PIPE.

BETWEEN TWO MATERIALS EXCEPT FOR

PIPE COMPOSITE PILE.

ADVANTAGES

BEST CONTROL DURING INSTALLATION.

CONSIDERABLE LENGTH CAN BE

NO DISPLACEMENT FOR OPEN END

PROVIDED AT COMPARATIVELY LOW

INSTALLATION. OPEN END PIPE BEST

COST. FOR WOOD COMPOSITE PILES.

AGAINST OBSTRUCTIONS. CAN BE

HIGH CAPACITY FOR PIPE AND HP

CLEANED OUT AND DRIVEN FURTHER.

COMPOSITE PILES. INTERNAL

HIGH LOAD CAPACITIES.

INSPECTION FOR PIPE COMPOSITE

EASY TO SPLICE.

PILES.

REMARKS

PROVIDES HIGH BENDING RESISTANCE

THE WEAKEST OF ANY MATERIAL USED

WHERE UNSUPPORTED LENGTH IS

SHALL GOVERN ALLOWABLE STRESSES

LOADED LATERALLY.

AND CAPACITY.

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-182

TABLE 1 (continued)
Design Criteria for Bearing Piles

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

AUGER-PLACED, PRESSURE-

PILE TYPE

INJECTED CONCRETE PILES

GENERAL NOTES

*)))))))))))))*))))))))))))))))))))))))))))))))))*))))))))))))))))))))))))))))))))*

CONSIDER FOR

30-60 FT.

1. STRESSES GIVEN FOR STEEL

LENGTH OF

PILES ARE FOR NONCORROSIVE

APPLICABLE

ACI-318

LOCATIONS, ESTIMATE POSSIBLE

MATERIAL

REDUCTION IN STEEL CROSS

SPECIFIC-

SECTION OR PROVIDE PROTECTION

ATIONS

FROM CORROSION.

2. LENGTHS AND LOADS INDICATED

MAXIMUM

3% OF 28-DAY STRENGTH OF

ARE FOR FEASIBILITY GUIDANCE

STRESSES.

CONCRETE

ONLY. THEY GENERALLY

REPRESENT TYPICAL CURRENT

CONSIDER FOR

35-70 TONS

PRACTICE, GREATER LENGTHS

DESIGN LOAD

ARE OFTEN USED.

3. DESIGN LOAD CAPACITY SHOULD

BE DETERMINED BY SOIL

MECHANICS PRINCIPLES,

LIMITING STRESSES IN PILES,

AND TYPE AND FUNCTION OF

STRUCTURE. SEE TEXT

DISADVANT-

MORE THAN AVERAGE DEPENDENCE ON

AGES

QUALITY WORKMANSHIP.

NOT SUITABLE THRU PEAT OR SIMILAR

HIGHLY COMPRESSIBLE MATERIAL.

REQUIRES RELATIVELY MORE EXTEN-

SIVE SUBSURFACE INVESTIGATION.

ADVANTAGES

ECONOMY.

COMPLETE NONDISPLACEMENT

MINIMAL DRIVING VIBRATION TO

ENDANGER ADJACENT STRUCTURES.

HIGH SKIN FRICTION.

GOOD CONTACT ON ROCK FOR END BEAR-

ING. CONVENIENT FOR LOW-HEADROOM

UNDERPINNING WORK.

VISUAL INSPECTION OF AUGERED MATER

-IAL. NO SPLICING REQUIRED.

REMARKS

BEST SUITED AS A FRICTION PILE.

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-183

TABLE 2
Characteristics of Common Excavated/Drilled Foundations

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

1. PIERS (also called Shafts)

a. Description and Procedures - Formed by drilling or excavating a

hole, removing the soil, and filling with concrete. Casing may be

necessary for stabilization, and/or to allow for inspection and may

or may not be pulled as the concrete is poured. Types include

straight shaft piers and belled or underreamed piers. Drilled

shaft diameters are typically 18 to 36 inches but can exceed 84

inches; belled diameters vary but are generally not larger than 3

times the diameter of the shaft. Excavated piers can be larger

(shaft diameters exceeding 12 feet with belled diameters exceeding

30 feet have been constructed). Lengths can exceed 200 feet.

Pier size depends on design load and allowable soil loads.

b. Advantages

o Completely non-displacement.

o Excavated material can be examined and bearing surface can be

visually inspected in cased piers exceeding 30 inches in diameter

(or smaller using TV cameras).

o Applicable for a wide variety of soil conditions.

o Pile caps usually not needed since most loads can be carried on a

single pier.

o No driving vibration.

o With belling, large uplift capacities possible.

o Design pier depths and diameters readily modified based on field

conditions.

o Can be drilled into bedrock to carry very high loads.

c. Disadvantages

o More than average dependence on quality of workmanship; inspection

required.

o Danger of lifting concrete when pulling casing can result in voids

or inclusions of soil in concrete.

o Loose granular soils below the water table can cause construction

problems.

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

)))-

7.2-184

TABLE 2 (continued)
Characteristics of Common Excavated/Drilled Foundations

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

o Bell usually cannot be formed in granular soils below the water

table.

o Small diameter piers (less than 30 inches) cannot be easily

inspected to confirm bearing and are particularly susceptible to

necking problems.

d. Typical Illustration

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

2. INTERNALLY-BRACED COFFERDAM IN OPEN WATER

a. Description and Procedures - Generally only applicable if structure

extends below mudline.

(1) Cofferdam constructed and dewatered before pouring of

foundation.

(a) Install cofferdam and initial bracing below water in

existing river/sea bottom. Cofferdam sheeting driven into

bearing strata to control underseepage.

(b) Pump down water inside cofferdam.

during excavation.

O'.

(d) Construct foundation within completed and dewatered

cofferdam.

(e) Guide piles or template required for driving cofferdams.

(f) Cofferdam designed for high water, ice forces, or load of

floating debris.

(g) Cellular wall or double-wall cofferdams will eliminate or

reduce required bracing system.

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-185

TABLE 2 (continued)
Characteristics of Common Excavated/Drilled Foundations

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

(2) Cofferdam excavated underwater

(a) Install cofferdam and initial bracing below water to

existing river/sea bottom.

(b) Excavate underwater and place additional bracing to

subgrade in bearing stratum.

balance expected hydrostatic uplift.

(d) Pump out cofferdam and erect remainder of foundation

structure.

(e), (f) and (g) same as dewatered cofferdam.

(h) Relief of water pressures below tremie slab may be used to

decrease weight of tremie slab.

b. Advantages - Generally more economical than caissons if foundation

is in less than 40 feet of water.

c. Disadvantages - Requires complete dewatering or tremie mat.

d. Typical Illustration

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-186

TABLE 2 (continued)

Characteristics of Common Excavated/Drilled Foundations

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

3. OPEN CAISSON

a. Description and Procedure - An open box or circular section with a

cutting shoe on its lower edge. The caisson is sunk into place

under its own weight by removal of the soil inside the caisson,

jetting on the outside wall is often used to facilitate the process.

(1) Caissons should be considered when one or more of the following

conditions exist:

(a) A substructure is required to extend to or below the

river/sea bed.

(b) The soil contains large boulders which obstruct

penetration of piles or drilled piers.

If these conditions do not exist the use of a caisson is not

warranted because it is generally more expensive than other types of

deep foundations. In open water, if the bearing stratum is less

than about 40 feet below the water surface, a spread footing

foundation constructed within cofferdams is generally less

expensive.

(2) General method of construction includes:

(a) Float caisson shell into position.

(b) Build up shell in vertical lifts and place fill within

shell until it settles to sea bottom.

so as to sink it through unsuitable upper strata.

(d) Upon reaching final elevation in bearing stratum, pour

tremie base.

(e) Provide anchorage or guides for caisson shell during

sinking.

(f) Floating and sinking operations can be facilitated by the

use of false bottoms or temporary domes.

(g) Dredging operations may be assisted by the use of jets or

airlifts.

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-187

TABLE 2 (continued)
Characteristics of Common Excavated/Drilled Foundations

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

Generally appropriate for depths exceeding 50 to 60 feet and

when final subgrade in the bearing stratum is not threatened

by uplift from underlying pervious strata.

b. Advantages - Feasibility of extending to great depths.

c. Disadvantages

o Bottom of the caisson cannot be thoroughly cleaned and inspected.

o Concrete seal placed in water is not as satisfactory as placed in

the dry.

o Soil directly under the haunched portion near the cutting edges

may require hand excavation by diver.

o Construction is slowed down if obstruction of boulders or logs is

encountered.

d. Typical Illustration

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

4. PNEUMATIC CAISSON

a. Description and Procedure - Similar to an open caisson but the box

is closed and compressed air is used to keep water and mud from

flowing into the box. Because of high costs, it is generally only

used on large projects where an acceptable bearing stratum cannot be

reached by open caisson methods because of excessive depth of water.

(1) Generally required for sinking to great depths where inflow of

material during excavation can be damaging to surrounding areas

and/or where uplift is a threat from underlying pervious

strata.

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-188

TABLE 2 (continued)
Characteristics of Common Excavated/Drilled Foundations

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

(2) General method of construction includes:

(a) Float caisson into position.

(b) Build, up on top of caisson in vertical lifts until the

structure settles to sea bottom.

compressed air when passing through unstable strata.

(d) Pour concrete base in the dry upon reaching final position

in the bearing stratum.

(e) Provide anchorage or guides for caisson during sinking.

For excavation in the dry, air pressure is generally made

equal to total head of water above bottom of caisson.

b. Advantages

o All work is done in the dry; therefore, controls over the

foundation preparation and materials are better.

o Plumbness of the caisson is easier to control as compared with the

open caisson.

o Obstruction from boulders or logs can be readily removed.

Excavation by blasting may be done if necessary.

c. Disadvantages

o The construction cost is high due to the use of compressed air.

o The depth of penetration below water is limited to about 120 feet

(50 psi). Higher pressures are beyond the endurance of the human

body.

o Use of compressed air restricts allowable working hours per man

and requires strict safety precautions.

d. Typical Illustration

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-189

TABLE 2 (continued)
Characteristics of Common Excavated/Drilled Foundations

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

5. CAISSON (Floating Caisson)

a. Description and Procedure - Essentially a cast-on-land floating

foundation sunk into position by backfilling.

(1) Used primarily for wharfs, piers, bulkheads, and breakwaters in

water not more than 40 feet deep.

(2) General construction method includes:

(a) Prepare subgrade at sea bottom by dredging, filling, or

combination of dredging and filling.

(b) Float caisson into position.

use of ballast.

(d) Provide anchorage or guides to protect floating caisson

against water currents.

(e) Backfill for suitable foundation should be clean granular

material and may require compaction in place under water.

b. Advantages

o The construction cost is relatively low.

o Benefit from precasting construction.

o No dewatering necessary.

c. Disadvantages

o The ground must be level or excavated to a level surface.

o Use is limited to only those conditions where bearing stratum is

close to ground surface.

o Provisions must be made to protect against undermining by scour.

o The bearing stratum must be adequately compacted to avoid adverse

settlements.

d. Typical Illustration

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-190

d. Earth Stabilization Columns. Many methods are available for forming
compression reinforcement elements (see DM-7.3, Chapter 2) including:

(1) Mixed-In-Place Piles. A mixed-in-place soil-cement or soil-lime
pile.

(2) Vibro-Replacement Stone Columns. A vibroflot or other device is
used to make a cylindrical, vertical hole which is filled with compacted
gravel or crushed rock.

(3) Grouted Stone Columns. This is similar to the above but
includes filling voids with bentonite-cement or water-sand-bentonite cement
mixtures.

(4) Concrete Vibro Columns. Similar to stone columns but concrete
introduced instead of gravel.

Section 3. BEARING CAPACITY AND SETTLEMENT

1. DESIGN PROCEDURES. The design of a deep foundation system should
include the following steps:

(1) Evaluate the subsurface conditions.

(2) Review the foundation requirements including design loads and
allowable settlement or deflection.

(3) Evaluate the anticipated construction conditions and procedures.

(4) Incorporate local experience and practices.

(5) Select appropriate foundation type(s) based on the above items,
costs, and comments on Tables 1 and 2.

(6) Determine the allowable axial foundation design loads based on an
evaluation of ultimate foundation capacity including reductions for group
action or downdrag if applicable, anticipated settlement and local
requirements and practices.

The axial load capacity of deep foundations is a function of the
structural capacity of the load carrying member (with appropriate reduction
for column action) and the soil load carrying capacity. Usually, the latter
consideration controls design. The methods available for evaluating the
ultimate axial load capacity are listed below. Some or all of these should
be considered by the design engineer as appropriate.

(a) Static analysis utilizing soil strength.

(b) Empirical analysis utilizing standard field soil tests.

7.2-191

(d) Full-scale load tests.

(e) Dynamic driving resistance.

(7) Determine design and construction requirements, and incorporate the
requirements into construction specifications.

Inspection of foundation construction should be considered an integral
part of the design procedures. Perform a pile test program as required. The
pile test can also be used as a design tool in item (6).

2. BEARING CAPACITY OF SINGLE PILE

a. Allowable Stresses. See Table 1 for allowable stresses within the
pile and quality requirements for pile materials. Allowable stresses should
be reduced for column action where the pile extends above firm ground, i.e.
through water and very soft bottom sediments.

b. Soil Support. The soil must be capable of supporting the element
when it is in compression, tension, and subject to lateral forces. The soil
support can be computed from soil strength data, determined by load tests,
and/or estimated from driving resistance. These determinations should
include the following stages:

(1) Design Stage. Compute required pile lengths from soil strength
data to determine bidding length and pile type.

(2) Early in Construction Stage. Drive test piles at selected
locations. For small projects where performance of nearby pile foundations
is known, base design length and load capacity on knowledge of the soil
profile, nearby pile performance, and driving resistance of test piles. On
large projects where little experience is available, perform load tests on
selected piles and interpret the results as shown in Figure 7.

(3) Throughout Construction Stage. Record driving resistance of
all piles for comparison with test piles and to insure against local weak
subsurface formations. Record also the type and condition of cushioning
material used in the pile hammer.

c. Theoretical Load Capacity. See Figure 1 for analysis of ultimate
load carrying capacity of single piles in homogeneous granular soils; for
pile in homogeneous cohesive soil see Figure 2 (upper panel right, Reference
2, The Bearing Capacity of Clays, by Skempton; remainder of figure,
Reference 3, The Adhesion of Piles Driven in Clay Soils, by Tomlinson).

(1) Compression Load Capacity. Compression load capacity equals
end-bearing capacity, plus frictional capacity on perimeter surface.

(2) Pullout Capacity. Pullout capacity equals the frictional force
on the perimeter surface of the pile or pier.

7.2-192

7.2-193

BEARING CAPACITY FACTORS - Nq

+))))))))))))))

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

+))))))))))))

)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),*

[phi][*]

(DEGREES]

*))))))))))))

*))))*))))*))))*))))*))))*))))*))))*))))*))))*))))*)))*))))*))))1*

(DRIVEN PILE

120

145

DISPLACE

MENT)

*)))))))))))))

*))))*))))*))))*))))*))))*))))*))))*))))*))))*))))*)))*))))*))))1*

[**]

(DRILLED

PIERS)

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-*

EARTH PRESSURE COEFFICIENTS K

AND K

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

PILE TYPE

*))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))*

DRIVEN SINGLE H-PILE

0.5 - 1.0

0.3 - 0.5

*))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))*

DRIVEN SINGLE DISPLACEMENT

PILE

1.0 - 1.5

0.6 - 1.0

*))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))*

DRIVEN SINGLE DISPLACEMENT

1.5 - 2.0

1.0 - 1.3

TAPERED PILE

*))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))*

DRIVEN JETTED PILE

0.4 - 0.9

0.3 - 0.6

*))))))))))))))))))))))))))))*)))))))))))))))))))*)))))))))))))))))))))))*

DRILLED PILE (LESS THAN

24" DIAMETER)

0.7

0.4

.))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

FRICTION ANGLE - [delta]

+)))))))))))))))))))))))))))))))))))))))))),

PILE TYPE

[delta]

*))))))))))))))))))))))))))))))))))))))))))*

STEEL 20 deg.

CONCRETE 3/4 [phi]

TIMBER 3/4 [phi]

.))))))))))))))))))))))))))))))))))))))))))-

[*] LIMIT [phi] TO 280 IF JETTING IS USED

[**] (A) IN CASE A BAILER OR GRAB BUCKET IS USED BELOW GROUND WATER TABLE,

CALCULATE END BEARING BASED ON [phi] NOT EXCEEDING 28 deg.

(B) FOR PIERS GREATER THAN 24-INCH DIAMETER, SETTLEMENT RATHER THAN BEARING

CAPACITY USUALLY CONTROLS THE DESIGN. FOR ESTIMATING SETTLEMENT, TAKE 50%

OF THE SETTLEMENT FOR AN EQUIVALENT FOOTING RESTING ON THE SURFACE OF

COMPARABLE GRANULAR SOILS. (CHAPTER 5, DM-7.1).

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

FIGURE 1 (continued)
Load Carrying Capacity of Single Pile in Granular Soils

7.2-194

7.2-195

7.2-196

(3) Drilled Piers. For drilled piers greater than 24 inches in
diameter settlement rather than bearing capacity may control. A reduced end
bearing resistance may result from entrapment of bentonite slurry if used to
maintain an open excavation to the pier's tip. Bells, or enlarged bases,
are usually not stable in granular soils.

(4) Piles and Drilled Piers in Cohesive Soils. See Figure 2 and
Table 3. Experience demonstrates that pile driving permanently alters
surface adhesion of clays having a shear strength greater than 500 psf (see
Figure 2). In softer clays the remolded material consolidates with time,
regaining adhesion approximately equal to original strength. Shear
strength for point-bearing resistance is essentially unchanged by pile
driving. For drilled piers, use Table 3 from Reference 4, Soils and
Geology, Procedures for Foundation Design of Buildings and Other Structures,
by lie Departments of Army and Air Force, for determining side friction.
Ultimate resistance to pullout cannot exceed the total resistance of reduced
adhesion acting over the pile surface or the effective weight of the soil
mass which is available to react against pullout. The allowable sustained
pullout load usually is limited by the tendency for the pile to move upward
gradually while mobilizing an adhesion less than the failure value.

Adhesion factors in Figure 2 may be very conservative for
evaluating piles driven into stiff but normally consolidated clays.
Available data suggests that for piles driven into normally to slightly
overconsolidated clays, the side friction is about 0.25 to 0.4 times the
effective overburden.

(5) Piles Penetrating Multi-layered Soil Profile. Where piles
penetrate several different strata, a simple approach is to add supporting
capacity of the individual layers, except where a soft layer may consolidate
and relieve load or cause drag on the pile. For further guidance on bearing
capacity when a pile penetrates layered soil and terminates in granular
strata see Reference 5, Ultimate Bearing Capacity of Foundations on Layered
Soils Under Inclined Loads, by Meyer off and Hanna, which consides the
ultimate bearing capacity of a deep member in sand underlying a clay layer
and for the case of a sand bearing stratum overlying a weak clay layer.

(6) Pile Buckling. For fully embedded piles, buckling usually is
not a problem. For a fully embedded, free headed pile with length equal to
or greater than 4T, the critical load for buckling is as follows (after
Reference 6, Design of Pile Foundations, by Vesic):

crit

= 0.78 T

f for L>/= 4T

where: P

crit

= critical load for buckling

f = coefficient of variation of lateral subgrade
reaction (see Figure 10)

T = relative stiffness factor (see Figure 10)

L = length of pile.

7.2-197

7.2-198

7.2-199

For piles with the head fixed against rotation and
translation, increase P

crit

by 13%. If the pile head is pinned (i.e.

prevented from translation but free to rotate), increase P

crit

by 62%.

For a partially embedded pile, assume a free standing column
fixed at depth 1.8T below the soil surface. Compute the critical buckling
load by methods of structural analysis. For such piles compute allowable
pile stresses to avoid buckling. For the case where the coefficient of
lateral subgrade reaction (K

) of the embedment soil is constant with

depth, calculate the depth of fixity as 1.4 [THE FOURTH RT] EI , where
K

EI is the flexural rigidity of the pile, B is pile width (diameter) and K

is defined in the units of Force/Length

. Buckling for a fully embedded

length of other pile types does not control pile stress. For further
guidance see Reference 6.

d. Empirical Bearing Capacity. Results from the Standard Penetration
Test, Static Cone penetrometer (Dutch Cone with friction sleeve), and
Pressuremeter have been correlated with model and full scale field tests on
piles and deep foundations so that empirical expressions are available to
estimate foundation capacities.

(1) Standard Penetration. Use of the Standard Penetration Test to
predict capacities of deep foundations should be limited to granular soils
and must be considered a crude estimate.

Tip Resistance of driven piles (after Reference 7, Bearing
Capacity and Settlement of Pile Foundations, by Meyerhof):

)

0.4 N D < /= q
q

ult

))))))))

)

where: N = CN - N

N = standard penetration resistance (blow/ft)
near pile tip

20
C

= 0.77 log

))

(for p>/= 0.25 TSF)

p = effective overburden stress at pile tip (TSF)

ult

= ultimate point resistance of driven pile (TSF)

)

N = average corrected Standard Penetration Resistance
near pile tip (blows/ft)

D = depth driven into granular bearing stratum (ft)

B = width or diameter of pile tip (feet)

= limiting point resistance (TSF), equal to

4N for sand and 3N for non-plastic silt.

7.2-200

For drilled piers, use 1/3 times q

ult

computed from the above

expression.

Use a factor of safety of 3 to compute allowable tip
resistance.

Skin Friction of driven piles:

)

N
f

))

< /= < f

where: N = average standard penetration along pile shaft

= ultimate skin friction for driven pile (TSF)

= limiting skin friction (for driven pile, f

= (TSF)

Use factor of safety of 3 for allowable skin friction.

For driven piles tapered more than 1 percent, use 1.5 times
above expression.

For drilled piers, use 50 percent of above expression

(2) The Cone Penetrometer. The Cone Penetrometer provides useful
information as a "model pile" and is best suited for loose to dense sands
and silts. Penetrometer results are not considered accurate for very dense
sands or deposits with gravel.

Point Resistance:

ult

= q

where: q

ult

= ultimate tip resistance for driven pile

= cone penetration resistance

Depth of penetration to granular bearing stratum is at least 10
times the pile tip width.

Shaft Resistance:

ult

= f

where: f

ult

= ultimate shaft friction of driven cylindrical pile

= unit resistance of local friction sleeve of static

penetrometer

Use factor of safety of 3 for allowable skin friction.

For drilled piers in cohesionless soil, use 1/2 of f

ult

based on the above expressions for driven piles.

7.2-201

(3) Pressuremeter. Results from pressuremeter tests can be used to
estimate design capacity of deep foundation elements. See Reference 8, The
Pressuremeter and Foundation Engineering, by Baguelin, et al., or Reference
9, Canadian Foundation Engineering Manual, by the Canadian Geotechnical
Society, for details of design correlation.

The pressuremeter method is useful in soft rock, weathered or
closely jointed rock, granular soils, and very stiff cohesive soils.
Results are generally not suitable in soft clays because of the disturbance
during drilling. The self-boring pressuremeter is designed to reduce this
problem.

e. Bearing Capacity from Dynamic Driving Resistance.

(1) General. The ultimate capacity of a pile may be estimated on
the basis of driving resistance during installation of the pile. The
results are not always reliable, and may over-predict or grossly
under-predict pile capacities, and therefore should be used with caution.
Use must be supported by local experience or testing. Dynamic resistance
based on the wave equation analysis is a more rational approach to
calculating pile capacities.

(2) Pile Driving Formulas:

(a) General. Because of the uncertainties of the dynamics of
pile driving, the use of formulas more elaborate than those in Table 4 is
not warranted. A minimum of three test piles should be driven for each
installation, with more tests if subsurface conditions are erratic.

(b) Control During Construction. The embedment of piles
should be controlled by specifying a minimum tip elevation on the basis of
the subsurface profile and driving tests or load tests, if available, and
also by requiring that the piles be driven beyond the specified elevation
until the driving resistance equals or exceeds the value established as
necessary from the results of the test piles. However, if the pile
penetration consistently overruns the anticipated depth, the basis for the
specified depth and driving resistance should be reviewed.

(c) Formulas. Dynamic pile driving formulas should not be
used as criteria for establishing load capacity without correlation with the
results of an adequate program of soil exploration. For critical structures
and where local experience is limited, or where unfamiliar pile types or
equipment are being used, load tests should be performed.

(3) Wave Equation Analysis. The wave equation analysis is based on
the theory of one dimensional wave propagation. For the analysis the pile
is divided into a series of masses connected by springs which characterize
the pile stiffness, and dashpots which simulate the damping below the pile
tip and along pile embedded length.

This method was first put into practical form in 1962
Reference 10, Pile Driving by the Wave Equation, by Smith). The wave
equation analysis provides a means of evaluating the suitability of the pile
stiffness to transmit driving energy to the tip to achieve pile penetration,
as well as the ability of pile section to withstand driving stresses without
damage. The results of the analysis can be interpreted to give the
following:

7.2-202

7.2-203

(a) Equipment compatibility: appropriate hammer size and
cushion.

(b) Driving stresses: plots of stress vs. set can be made to
evaluate the potential for pile overstress.

The soil is modeled by approximating the static resistance (quake),
the viscous resistance (damping), and the distribution of the soil
resistance along the pile. The assigned parameter for springs and dashpots
cannot be related to routinely measured soil parameters which constitutes
the major draw back of the wave equation analysis. The input for the
driving system is provided by the anticipated hammer performance,
coefficient of restitution of the cushion, and stiffness of the pile.
Computer programs are available to perform the lengthy calculations.

(4) Case Method. The wave equation analysis can be used in
conjunction with field measurements by using the Case Method (Reference 11,
Soil Resistance Predictions from Pile Dynamics, by Rausche, et al.). This
procedure electronically measures the acceleration and strain near the
top of the pile, and by using the wave equation analysis estimates the
static soil resistance for each blow of the hammer. Energy transferred to
the pile is computed by integrating the product of force and velocity. A
distribution of the soil resistance along the pile length is assumed and the
wave equation analysis is performed. The assumed soil strength parameters
are checked against the measured force at the pile top and these are then
adjusted to result in an improved match between the analytical and measured
pile force at the top.

3. BEARING CAPACITY OF PILE GROUPS.

a. General. The bearing capacity of pile groups in soils is normally
less than the sum of individual piles in the group and must be considered in
design. Group efficiency is a term used for the ratio of the capacity of a
pile group to the sum of the capacities of single piles at the same depth in
the same soil deposit. In evaluating the performance of pile groups in
compression, settlement is a major consideration. Expressions for
estimating uplift resistance of pile groups are included in this section.

b. Group Capacity in Rock. The group capacity of piles installed to
rock is the number of members times the individual capacity of each member.
Block failure is a consideration only if foundations are on a sloping rock
formation, and sliding may occur along unfavorable dipping weak planes.
The possibility of such an occurrence must be evaluated from the site
geology and field exploration.

c. Group Capacity in Granular Soil. Piles driven into cohesionless
soil in a group configuration act as individual piles if the spacing is
greater than 7 times the average pile diameter. They act as a group at
close spacings. Center to center spacing of adjacent piles in a group
should be at least two times the butt diameter.

7.2-204

Block failure of a pile group in granular soils is not a design
consideration provided each individual pile has an adequate factor of safety
against bearing failure and the cohesionless soil is not underlain by a
weaker deposit. In loose sand and/or gravel deposits, the load carrying
capacity of an individual pile may be greater in the group than single
because of densification during driving. This increased efficiency should
be included in design with caution, and only where demonstrated by field
experience or tests.

The ultimate capacity of a pile group founded in dense cohesionless
soil of limited thickness underlain by a weak deposit is the smaller of:

(1) sum of the single pile capacities

(2) block failure of a pier equivalent in size to the piles and
enclosed soil mass, punching through the dense deposit into the underlying
weak deposit (Reference 12, Ultimate Bearing Capacity of Footings on Sand
Layer Overlying Clay, by Meyerhof).

d. Group Capacity in Cohesive Soil. Estimate the group capacity using
the method in Figure 3 (upper panel, Reference 13, Experiments with Model
Piles in Groups, by Whitaker).

e. Uplift Resistance of Groups.

(1) Granular Soil. Ultimate uplift resistance of pile group is
lesser of:

(a) Sum of skin friction on the piles in the group (no
reduction for tapered piles), use a factor of safety of 3.0.

(b) Effective weight of block of soil within the group and
within a 4 vertical on 1 horizontal wedge extending up from pile
tips - weight of piles assumed equal to volume of soil they displace.
Factor of safety should be unity.

(2) Cohesive Soil. Ultimate uplift resistance of pile group is the
lesser of:

(a) Sum of skin friction on the piles in the group

(b) T

= L (B + A) C + W

where: T

= ultimate uplift resistance of pile group

A = length of group

B = width of group

L = depth of soil block below pile cap

C = average undrained strength of soil around the sides of the
group

= weight of piles, pile cap, and block of soil enclosed by the

piles.

7.2-205

7.2-206

Factors of Safety: 2 for short-term loads, 3 for sustained
uplifting loading.

4. SETTLEMENTS OF PILE FOUNDATIONS

a. Single Pile. The settlement at the top of pile can be broken down
into three components (after Reference 6).

(1) Settlement due to axial deformation of pile shaft; Ws

L
Ws = (Q

+ [alpha]

)

where: Q

= point load transmitted to the pile tip in the working stress

range.

= shaft friction load transmitted by the pile in the working

stress range (in force units)

[alpha]

= 0.5 for parabolic or uniform distribution of shaft

friction

0.67 for triangular distribution of shaft friction starting
from zero friction at pile head to a maximum value at pile
point

0.33 for triangular distribution of shaft friction
starting from a maximum at pile head to zero at the
pile point.

L = pile length

A = pile cross sectional area

= modulus of elasticity of the pile

(2) Settlement of pile point caused by load transmitted at the
point W

)))))))))

where: C

= empirical coefficient depending on soil type and

method of construction, see Table 5

B = pile diameter

= ultimate end bearing capacity

(3) Settlement of pile points caused by load transmitted along the
pile shaft, W

;

))))))))

7.2-207

TABLE 5
Typical[*] Values of Coefficient C

for Estimating

Settlement of a Single Pile

+))))))))))))))))))))))))))))0))))))))))))))))))))))))))0)))))))))))))))))))))),

Soil Type

Driven Piles

Bored Piles

/))))))))))))))))))))))))))))3))))))))))))))))))))))))))3))))))))))))))))))))))1

Sand (dense to loose)

0.02 to 0.04

0.09 to 0.18

Clay (stiff to soft)

0.02 to 0.03

0.03 to 0.06

Silt (dense to loose)

0.03 to 0.05

0.09 to 0.12

/))))))))))))))))))))))))))))2))))))))))))))))))))))))))2)))))))))))))))))))))

*
*

[*] Bearing stratum under pile tip assumed to extend at least 10 pile

*
*

diameters below tip and soil below tip is of comparable or higher

*
*

stiffness.

*
.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))
)-

7.2-208

where: C

= (0.93 + 0.16 D/B) C

D = embedded length

(4) Total settlement of a single pile, W

= W

+ W

b. Settlement of Pile Group in Granular Soils. Compute the group
settlement W

based on (after Reference 6):

+))))

)

= W

B/B

)

where: B = the smallest dimension of pile group

B = diameter of individual pile

= Settlement of a single pile estimated or determined

from load tests

c. Settlement of Pile Groups in Saturated Cohesive Soils. Compute the
group settlement as shown in Figure 4.

d. Limitations. The above analyses may be used to estimate settlement,
however, settlement estimated from the results of load tests are generally
considered more accurate and reliable.

5. NEGATIVE SKIN FRICTION.

a. General. Deep foundation elements installed through compressible
material can experience "downdrag" forces or negative skin friction along
the shaft which results from downward movement of adjacent soil relative to
the pile. Negative skin friction results primarily from consolidation of a
soft deposit caused by dewatering or the placement of fill.

Negative skin friction is particularly severe on batter pile
installations because the force of subsiding soil is large on the outer side
of the batter pile and soil settles away from the inner side of the pile.
This can result in bending of the pile. Batter pile installations should be
avoided where negative skin friction is expected to develop.

b. Distribution of Negative Skin Friction on Single Pile. The
distribution and magnitude of negative skin friction along a pile shaft
depends on:

(1) relative movement between compressible soil and pile shaft;

(2) relative movement between upper fill and pile shaft;

(3) elastic compression of pile under working load;

(4) rate of consolidation of compressible soils.

7.2-209

7.2-210

Negative skin friction develops along that portion of the pile shaft
where settlement of the adjacent soil exceeds the downward displacement of
the shaft. The "neutral point" is that point of no relative movement
between the pile and adjacent soil. Below this point, skin friction acts to
support pile loads. The ratio of the depth of the neutral point to the
length of the pile in compressible strata may be roughly approximated as
0.75. The position of the neutral point can be estimated by a trial and
error procedure which compares the settlement of the soil to the
displacement of adjacent sections of the pile. (For further guidance see
Reference 14, Pile Design and Construction Practice, by Tomlinson.)

Observations indicate that a relative downward movement of 0.6 inch
is expected to be sufficient to mobilize full negative skin friction
(Reference 6).

c. Magnitude of Negative Skin Friction on Single Pile. The peak
negative skin friction in granular soils and cohesive soils is determined as
for positive skin friction.

The peak unit negative skin friction can also be estimated from
(after Reference 15, Prediction of Downdrag Load at the Cutler Circle
Bridge, by Garlanger):

fn= [beta]P

where: f

= unit negative skin friction (to be multiplied by

area of shaft in zone of subsiding soil relative to pile)

= effective vertical stress

[beta] = empirical factor from full scale tests

Soil [beta]

))))

)))))))))))

Clay 0.20 - 0.25
Silt 0.25 - 0.35
Sand 0.35 - 0.50

d. Safety Factor for Negative Skin Friction. Since negative skin
friction is usually estimate on the safe side, the factor of safety
associated with this load is usually unity. Thus:

ult

all

))))))

)

where: Q

all

= allowable pile load

ult

= ultimate pile load

= factor of safety

= ultimate negative skin friction load

7.2-211

For further discussion of factor of safety in design including
transient loads, see Reference 16, Downdrag on Piles Due to Negative Skin
Friction, by Fellenius.

e. Negative Skin Friction on Pile Groups. The negative skin friction
on a pile group does not usually exceed the total weight of fill and/or
compressible soil enclosed by the piles in the group. For the case of
recent fill underlain by a compressible deposit over the bearing stratum:

total

< /= W + (B)(L) ([gamma]

+ [gamma]

)

where: P

total

= total load on pile group

W = working load on pile group

B = width of pile group

L = length of pile group

[gamma]

, [gamma]

= effective unit weight of fill and underlying

compressible soil respectively

, D

= depth over which fill and compressible soil

is moving downward relative to the piles

f. Reduction of Negative Skin Friction. Several methods have been
developed to reduce the expected negative skin friction on deep foundations.
These include:

(a) Use of slender piles, such as H-sections, to reduce shaft area
subject to drag.

(b) Predrilled oversized hole through compressible material prior
to insertion of pile (resulting annular space filled with bentonite slurry
or vermiculite)

(d) Coat pile shaft with bitumen to allow slippage.

Bitumen compounds which can be sprayed or poured on clean piles are
available to reduce negative skin friction. Coatings should be applied only
to those portions of the pile anticipated to be within a zone of subsidence
and the lower portion of the pile (at least ten times the diameter) should
remain uncoated so that the full lower shaft and point resistance may be
mobilized. Reductions of negative friction of 50% or greater have been
measured for bituminous coatings on concrete and steel piling (see Reference
17, Reducing Negative Skin Friction with Bitumen Layers, by Claessen and
Horvat, and Reference 18, Reduction of Negative Skin Friction on Steel Piles
to Rock, by Bjerrum, et al.).

7.2-212

Section 4. PILE INSTALLATION AND LOAD TESTS

1. PILE INSTALLATION.

a. General Criteria. See Table 6.

b. Installation Techniques. Table 7 summarizes the more common
supplementary procedures and appurtenances used in driven pile
installations.

c. Pile Driving Hammers. Table 8 (Reference 6) summarizes the
characteristics of the more common types of hammers in use in the U.S.
Figure 5 shows principal operation of pile drivers (modified from Reference
6):

(1) Drop Hammer. Generally, it is only appropriate on small,
relatively inaccessible jobs due to their slow rate of blows.

(2) Single Action Steam or Air Hammers. Blow rate is higher than
drop hammer with maximum speeds generally ranging from about 35 to 60 blows
per minute. Single acting hammers have an advantage over double acting
hammers when driving piles in firm cohesive soils since the slower rate
allows the soil and pile to relax before striking the next blow; thereby
giving greater penetration per blow. In driving batter piles, single acting
hammers can lose considerable energy due to the shortening fall and
increases in friction.

(3) Double Acting Steam or Air Hammers. They provide a blow rate
nearly double that of the single acting hammers and lose less energy driving
batter piles. They are generally best suited for driving piles in
granular soils or in soft clays. The energy per blow delivered by a
double-acting hammer decreases rapidly as its speed of operation drops below
the rated speed.

(4) Diesel Hammers. They have a relatively low fuel consumption,
operate without auxiliary equipment, and can operate at low temperatures and
are more efficient for driving batter piles. Maximum blow rates are about
35 to 60 blows per minute for single acting and about 80 to 100 blows per
minute for double acting. Diesel hammers operate best in medium to hard
ground; in soft ground the resistance and resulting compression may be too
low to ignite the fuel.

(5) Vibratory Hammers. They are best suited to wet soils and low
displacement piles but occasionally have been used successfully in cohesive
soils and with high displacement piles. They can also be effective in
extracting piles. When conditions are suitable, vibratory hammers have
several advantages over impact hammers including lower driving vibrations,
reduced noise, greater speed of penetration and virtually complete
elimination of pile damage. However, there is the possibility that the pile
may not be efficiently advanced, obstructions generally can not be
penetrated, and there is no generally accepted method of determining
ultimate pile capacity based on the rate of penetration.

7.2-213

7.2-214

7.2.-215

7.2-216

7.2-217

7.2-218

TABLE 8
Impact and Vibratory Pile-Driver Data

+)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

1. IMPACT PILE HAMMER

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))1

Weight

Rated[**] Stroke Striking Total

Energy Make of Blows at Rated Parts Weight

Kip - ft. Hammer[*] Model No. Types[*] per min Energy Kips Kips

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

180.0 Vulcan 060 S-A 62 36 60.0 121.0

130.0 MKT S-40 S-A 55 39 40.0 96.0

120.0 Vulcan 040 S-A 60 36 40.0 87.5

113.5 S-Vulcan 400C Diff. 100 16.5 40.0 83.0

97.5 MKT S-30 S-A 60 39 30.0 86.0

79.6 Kobe K42 Dies. 52 98 9.2 22.0

60.0 Vulcan 020 S-A 60 36 20.0 39.0

60.0 MKT S20 S-A 60 36 20.0 38.6

56.5 Kobe K32 Dies. 52 98 7.0 15.4

50.2 S-Vulcan 200C Diff. 98 15.5 20.0 39.0

48.7 Vulcan 016 S-A 60 36 16.2 30.2

48.7 Raymond 0000 S-A 46 39 15.0 23.0

44.5 Kobe K22 Dies. 52 98 4.8 10.6

42.0 Vulcan 014 S-A 60 36 14.0 27.5

40.6 Raymond 000 S-A 50 39 12.5 21.0

39.8 Delmag D-22 Dies. 52 N/A 4.8 10.0

37.5 MKT S14 S-A 60 32 14.0 31.6

36.0 S-Vulcan 140C Diff. 103 15.5 14.0 27.9

32.5 MKT S10 S-A 55 39 10.0 22.2

32.5 Vulcan 010 S-A 50 39 10.0 18.7

32.5 Raymond 00 S-A 50 39 10.0 18.5

32.0 MKT DE-40 Dies. 48 96 4.0 11.2

30.2 Vulcan OR S-A 50 39 9.3 16.7

26.3 Link-Belt 520 Dies. 82 43.2 5.0 12.5

26.0 MKT C-8 D-A 81 20 8.0 18.7

26.0 Vulcan 08 S-A 50 39 8.0 16.7

26.0 MKT S8 S-A 55 39 8.0 18.1

24.4 S-Vulcan 80C Diff. 111 16.2 8.0 17.8

24.4 Vulcan 8M Diff. 111 N/A 8.0 18.4

24.3 Vulcan 0 S-A 50 39 7.5 16.2

24.0 MKT C-826 D-A 90 18 8.0 17.7

22.6 Delmag D-12 Dies. 51 N/A 2.7 5.4

22.4 MKT DE-30 Dies. 48 96 2.8 9.0

24.4 Kobe K13 Dies. 52 98 2.8 6.4

19.8 Union K13 D-A 111 24 3.0 14.5

19.8 MKT 11B3 D-A 95 19 5.0 14.5

19.5 Vulcan 06 S-A 60 36 6.5 11.2

19.2 S-Vulcan 65C Diff. 117 15.5 6.5 14.8

18.2 Link-Belt 440 Dies. 88 36.9 4.0 10.3

))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-219

TABLE 8 (continued)

Impact and Vibratory Pile-Driver Data

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

Weight

Rated[**] Blows Stroke Striking Total

Energy Make of Model per at Rated Parts Weight

Kip - ft. Hammer[*] No. Types[*] min Energy Kips Kips

/)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))1

16.2 MKT S5 5-A 60 39 5.0 12.3

16.0 MKT DE-20 Dies. 46 96 2.0 6.3

16.0 MKT CS Comp. 110 18 5.0 11.8

15.1 S-Vulcan 50C Diff. 120 15.5 5.0 11.7

15.1 Vulcan 5M Diff. 120 15.5 5.0 12.9

15.0 Vulcan 1 5-A 60 36 5.0 10.1

15.0 Link-Belt 312 Dies. 100 30.9 3.8 10.3

13.1 MKT 10B3 D-A 105 19 3.0 10.6

12.7 Union 1 D-A 125 21 1.6 10.0

9.0 Delmag D5 Dies. 51 N/A 1.1 2.4

9.0 MKT C-3 D-A 130 16 3.0 8.5

9.0 MKT S3 5-A 65 36 3.0 8.8

8.8 MKT DE-10 Dies. 48 96 11.0 3.5

8.7 MIT 9B3 D-A 145 17 1.6 7.0

8.2 Union 1.5A D-A 135 18 1.5 9.2

8.1 Link-Belt 180 Dies. 92 37.6 1.7 4.5

7.2 Vulcan 2 5-A 70 29.7 3.0 7.1

7.2 S-Vulcan 30C Diff. 133 12.5 3.0 7.0

7.2 Vulcan 3M Diff. 133 N/A 3.0 8.4

6.5 Link-Belt 105 Dies. 94 35.2 1.4 3.8

4.9 Vulcan DGH900 Diff. 238 10 .9 5.0

3.6 Union 3 D-A 160 14 .7 4.7

3.6 MKT 7 D-A 225 9.5 .8 5.0

.4 Union 6 D-A 340 7 .1 .9

.4 Vulcan DGH100A Diff. 303 6 .1 .8

.4 MKT 3 D-A 400 5.7 .06 .7

.3 Union 7A D-A 400 6 .08 .5

/)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))*

[*] Codes

MKT - McKiernan-Terry D-A - Double-Acting

S-Vulcan - Super-Vulcan Diff. - Differential

S-A - Single-Acting Dies. - Diesel

Comp. - Compound

[**]In calculations of pile capacities by dynamic formula, effective energy

delivered by hammer should be used. Hammer energy is affected by pressures

used to operate the hammer, stroke rate, etc. Double-acting, differential,

and diesel hammers may operate at less than rated energies; double-acting

hammers deliver significantly less than rated energy when operated at less

than rated speed. Consult manufacturers.

TABLE 8 (continued)
Impact and Vibratory Pile-Driver Data

+))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))),

2. VIBRATORY DRIVERS

*)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))1

Frequency Force Kips[***],

Total Weight Available Range Frequency

Make Model Kips HP cps cps

*)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))1

Foster 2-17 6.2 34 18-21

(France) 2-35 9.1 70 14-19 62/19

2-50 11.2 100 11-17 101/17

Menck MVB22-30 4.8 50 48/

(Germany) MVB65-30 2.0 7.5 14/

MVB44-30 8.6 100 97/

Muller MS-26 9.6 72

(Germany) MS-26D 16.1 145

Uraga VHD-1 8.4 40 16-20 43/20

(Japan) VHD-2 11.9 80 16-20 86/20

VHD-3 15.4 120 16-20 129/20

Bodine B 22 1000 0-150 63/100 - 175/100

(USA)

(Russia) BT-5 2.9 37 42 48/42

VPP-2 4.9 54 25 49/25

100 4.0 37 13 44/13

VP 11.0 80 6.7 35/7

VP-4 25.9 208 198/

[***] Forces given are present maximums. These can usually be raised or lowered

by changing weights in the oscillator.

.)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))-

7.2-221

7.2-222

d. Inspection Guidelines. See Table 6 for general guidance and
Reference 19, Inspectors' Manual for Pile Foundations, by the Deep
Foundation Institute.

(1) Driven Piles. The inspector should normally assess the
performance of the driving equipment, record the driving resistances,
particularly the final set (net penetration per blow), record the driven
depth and tip elevation, and continually observe the pile for evidence of
damage or erratic driving. The criteria for termination of pile driving is
normally a penetration resistance criteria or a required depth of
penetration. Normally, a set criteria would be used for end bearing piles
or piles where soil freeze is not a major factor while penetration criteria
would be more appropriate for friction piles, piles into clay, and/or when
soil freeze is a major factor.

(a) Timber Piles. (Reference 20, AWPI Technical Guidelines
for Pressure-Treated Wood, Timber Piling, and ASTM Standard D25, Round
Timber Piles.) Site Engineer/Inspector should check the following items:

- Overstressing at the top of pile, usually visible
brooming.

- Properly fitted driving cap.

- Straightness.

- Sound wood free of decay and insect attack.

- Pressure treatment.

- Low frequency of knots.

(b) Concrete Piles. (Reference 21, Recommendations for
Design, Manufacture, and Installation of Concrete Piles, by the American
Concrete Institute.) Site Engineer/Inspector should check the following
items:

- That pile length, geometry, thickness, and straightness
conforms to specifications.

- Note extent, amount, and location of spilling or
cracking in the pile during driving and pick up, and
set.

- Thickness and type of cushion - should comply with
specification.

- Compliance with applicable codes and specifications.

- Structural damage to pile due to over-driving/
overstressing.

- Pile orientation conforms to the plans.

7.2-223

(2) Drilled Piers. Minimum requirements for proper inspection of
drilled shaft construction are as follows:

(a) For Dry or Casing Method of Construction;

- A qualified inspector should record the material types
being removed from the hole as excavation proceeds.

- When the bearing soil has been encountered and
identified and/or the designated tip elevation has been
reached, the shaft walls and base should be observed
for anomalies, unexpected soft soil conditions,
obstructions or caving.

- Concrete placed freefall should not be allowed to hit
the sidewalls of the excavation.

- Structural stability of the rebar cage should be
maintained during the concrete pour to prevent
buckling.

- The volume of concrete should be checked to ensure
voids did not result during extraction of the casing.

- Concrete must be tremied into place with an adequate
head to displace water or slurry if groundwater has
entered the bore hole.

- Pulling casing with insufficient concrete inside should
be restricted.

- Bottom of hole should be cleaned.

(b) For Slurry Displacement Method of Construction.

- A check on the concrete volume and recording the
material types and depth of shaft apply the same as
above.

- The tremie pipe should be watertight and should be
fitted with some form of valve at the lower end.

(3) Caissons on Rock. Inspection of caisson bottom is usually
accomplished by either:

(a) Probing with a 2-1/2" diameter probe hole to a minimum of
8 feet or 1.5 times the caisson shaft diameter (whichever is larger).

(b) Visual inspection by a qualified geologist at caisson
bottom with proper safety precautions or from the surface utilizing a
borehole camera. The purpose of the inspection is to determine the extent
of seams, cavities and fractures. The allowable cumulative seam thickness
within the probe depth varies depending on performance criteria. Values as
low as 1/4" of cumulative thickness can be specified for the top 1/2
diameter.

7.2-224

e. Installation Guidelines.

(1) Driven Piles.

(a) For pile groups, drive interior piles first to avoid hard
driving conditions, overstressing, and to minimize heave.

(b) Make sure pile driving caps and/or cushions are
appropriate.

(d) Cheek for proper alignment of the driving head.

(e) If the pile suddenly changes directions or a substantially
reduced driving resistance is noted, the pile is probably broken.

Table 9 summarizes some of the common installation problems and
recommended procedures. Table 10 (Reference 22, Drilled Shafts: Design and
Construction Guideline Manual, Vol 1: Construction Procedures and Design
for Axial Load, by Reese and Wright) summarizes some of the more common
installation problems and procedures for drilled piers.

(2) Performance Tolerance. It is normal practice to tailor the
specifications to particular site conditions and to structural performance
criteria. In many applications the following criteria may apply:

(a) Allowable Deviation from Specified Location. In the
absence of another over-riding project specification criteria, use 4 inches.
Consider the technical feasibility of increasing to more than 4 inches
for caps with 4 piles or less.

(b) Allowable out-of-vertical. In the absence of the
overriding project specification criteria, use 2% provided that the
allowable deviation is not exceeded. Values of 4%, 2% and 1/4 inch out of
plumb have been used.

(c) Allowable Heave Before Redriving. Require redriving of
piles if heave exceeds 0.01 feet for essentially friction piles, or any
detectable heave if piles are known to be essentially end-bearing.

(d) Minimum Distance of Pile Being Driven from Fresh Concrete.
In the absence of over-riding project specification criteria, use 15 feet.
Values of 10 feet to 50 feet have been used in practice.

7.2-225

7.2-226

TABLE 10
Drilled Piers: Construction Problems

+)))))))))))))))))))))))))))))))))))0))))))))))))))))))))))))))))))))))))))))))))),

Problem

Solution

*)))))))))))))))))))))))))))))))))))3)))))))))))))))))))))))))))))))))))))))))))))*

Pouring concrete through water

Removal of water by hailing or use of

tremie

Segregation of concrete during

If free-fall is employed, exercising care

placing

to see that concrete falls to final

location without striking anything, or use

of tremie

Restricted flow of concrete

Designing of rebar cage with adequate

through or around rebar cage

spacing for normal concrete (all clear

spaces at least three times the size of

largest aggregate) or use of special mix

with small-sized coarse aggregate

Torsional buckling of rebar

Strengthening rebar cage by use of

cage during concrete placement

circumferential bands welded to lower

with casing method

portion of cage, use of concrete with

improved flow characteristics, use of

retarder in concrete allowing casing to be

pulled very slowly

Pulling casing with

Always having casing extending above

insufficient concrete inside

ground surface and always having casing

filled with a sufficient head of concrete

with good flow characteristics before

casing is pulled

Weak soil or undetected cavity

Requiring exploration to a depth of a few

beneath base of foundation

diameters below the bottom of the

excavation

Deformation or collapse of soil

Such problems are readily detected by

even the minimums of inspection

.)))))))))))))))))))))))))))))))))))2)))))))))))))))))))))))))))))))))))))))))))))-

7.2-227

2. PILE LOAD TEST.

a. General. The results of pile load tests are the most reliable means
of evaluating the load capacity of a deep foundation. Load tests can be
performed during the design phase as a design tool and/or during
construction to verify design loads. Pile load tests should be considered
for large and/or critical projects, for pile types and soil conditions for
which there is limited previous local experience, when proposed design loads
exceed those normally used, and for other design/site conditions such as the
need to use lower than specified factor of safety in the design.

The types of pile load tests normally performed include:

(1) Standard Loading Procedures or Slow Maintained-Load Test
Method. For procedure, refer to ASTM Standard D3689, Individual Piles under
Static Axial Tensile Load. It is the most common load test currently used.
It is a long duration test (typically 70 hours or longer) loaded to 200
percent of the design load, or to failure. To determine curve of plastic
deformation, the test procedure should be altered to include at least three
unload-reload cycles. This procedure is described in ASTM Standard D1143,
Pile Under Axial Compressive Load.

(2) Quick Maintained-Load Test Method. For procedure, refer to
ASTM Standard D1143. This is a short duration test, typically 1 to 4 hours,
generally loaded to 300 percent of the design load or failure. It is
suitable for design load test and can be effectively used for load proof
testing during construction.

(3) Constant Rate of Penetration (or Uplift) Test Method. A
displacement-controlled method. For procedure, refer to ASTM Standard D1143
or ASTM Standard D3689. It is a short duration test, typically 2 to 3
hours, and may require special loading equipment as described in Reference
23, A Device for the Constant Rate of Penetration Test for Piles by Garneau
and Samson. This method is recommended for testing piles in cohesive soils
and for all tests where only the ultimate capacity is to be measured. The
method can provide information regarding behavior of friction piles and is
well suited for load tests during design.

b. Interpretation of Results. There are numerous procedures for
interpretation of pile load test results including those specified by local
building codes. A deflection criteria is normally used to define failure.
In the absence of an over-riding project specification criteria, use 3/4
inch net settlement at twice the design load. Values of 1/4 and 1 inch at
twice the design load and 1/4 inch at three times the design load have been
used. Figure 6 presents a procedure for determining the failure load based
on a permanent set of 0.15 + D/120 inches (where D is the pile diameter
in inches). This procedure can be used for either of the three test methods
presented above.

Where negative skin friction (downdrag) may act on the pile, only
load carried by the pile below the compressible zone should be considered.
This may be determined by minimizing shaft resistance during the load test
(e.g., predrilling oversized hole, case and clean, using bentonite slurry,
etc.) or by measuring movement of tip directly by extension rods attached to
the pile tip and analyzing test results in accordance with Figure 7.

7.2-228

7.2-229

c. Pullout Tests. Methods of determining failure load for tension load
tests vary depending on the tolerable movement of the structure. In
general, failure load is more easily defined than for compression load tests
since available resistance generally decreases more distinctly after
reaching failure. Failure load may be taken as that value at which upward
movement suddenly increases disproportionately to load applied, i.e. the
point of sharpest curvature on the load-displacement curve.

d. Lateral Load Tests. Lateral load tests are usually performed by
jacking apart two adjacent pile and recording deflections of the piles for
each load increment. See Reference 24, Model Study of Laterally Loaded
Pile, by Davisson and Salley, for further guidance. In some applications
testing of a pile group may be required.

e. Other Comments. A response of a driven pile in a load test can be
greatly affected by the time elapsed between driving and testing. In most
cases, a gain in pile bearing capacity is experienced with time and is
governed by the rate of dissipation of excess pore water pressures generated
by driving the pile throughout the surrounding soil mass. This is
frequently termed "freezing." The time required for the soil to regain its
maximum shear strength can range from a minimum of 3 to 30 days or longer.
The actual required waiting period may be determined by redriving piles or
from previous experience. Generally, however, early testing will result in
an underestimate of the actual pile capacity especially for piles deriving
their capacity from saturated cohesive soils.

Piles driven through saturated dense fine sands and silts may
experience loss of driving resistance after periods of rest. When redriven
after periods of rest the driving resistance (and bearing capacity) will be
less compared to the initial driving resistance (and capacity). This
phenomenon is commonly referred to as relaxation.

Section 5. DISTRIBUTION OF LOADS ON PILE GROUPS

1. VERTICAL PILE GROUPS.

a. Eccentric Vertical Loading. Distribution of design load on piles in
groups is analyzed by routine procedures as follows:

(1) For distribution of applied load eccentric about one or two
axes, see Reference 6.

(2) Overload from eccentricity between applied load and center of
gravity of pile group shall be permitted up to 10 percent of allowable
working load when a safety factor of 2-1/2 to 3 is available for the working
load.

(3) Overload from wind plus other temporary live loads up to 33
percent of the allowable working load is permitted, when a safety factor of
2-1/2 to 3 is available for the working load.

(4) Except in unusual circumstances, all bearing piles in a group
shall be of the same type, and of equal load capacity.

7.2-230

7.2-231

2. GROUPS WITH VERTICAL AND BATTER PILES. Analyze distribution of pile
loads according to criteria in Reference 25, Pile Foundations, by Chellis.
The following limitations apply:

(1) Assume inclination of batter piles no flatter than 1 horizontal
to 3 vertical unless special driving equipment is specified.

(2) When batter piles are included in a group, no allowance is made
for possible resistance of vertical piles to horizontal forces.

(3) For analysis of loads on piles in relieving platforms, see
Reference 26, American Civil Engineering Practice, Vol. 1, by Abbett.

(4) For analysis of batter pile anchorage for tower guys, see
Figure 8.

Section 6. DEEP FOUNDATIONS ON ROCK

1. GENERAL. For ordinary structures, most rock formations provide an ideal
foundation capable of supporting large loads with negligible settlement.
Normally, the allowable loads on piles driven into rock are based on pile
structural capacity while the allowable bearing pressures for footings/piers
on rock are based on a nominal values of allowable bearing capacity (see
Chapter 4).

There are however certain unfavorable rock conditions (e.g., cavernous
limestone, see DM-7.1, Chapter 1) which can result in excessive settlement
and/or failure. These potential hazards must be considered in the design
and construction of foundations on rock.

2. PILES DRIVEN INTO ROCK. Piles driven into rock normally meet refusal at
a nominal depth below the weathered zone and can be designed based on the
structural capacity of the pile imposed by both the dynamic driving
stresses and the static stresses. Highly weathered rocks such as decomposed
granite or limestone and weakly cemented rocks such as soft clay-shales can
be treated as soils.

The possibility of buckling below the mudline should be evaluated for
high capacity pile driven through soft soils into bedrock (see Reference 27,
The Design of Foundations for Buildings, by Johnson and Kavanaugh).

3. ALLOWABLE LOADS ON PIERS IN ROCK. Piers drilled through soil and a
nominal depth into bedrock should be designed on the basis of an allowable
bearing pressure given in Chapter 4 or other criteria (see Reference 28,
Foundation Engineering, by Peck, et al.). Piers are normally drilled a
nominal depth into the rock to ensure bearing entirely on rock and to extend
the pier through the upper, more fractured zones of the rock. Increase in
allowable bearing with embedment depth should be based on encountering more
competent rock with depth.

7.2-232

7.2-233

Rock-socketed drilled piers extending more than a nominal depth into rock
derive capacity from both shaft resistance and end bearing. The proportion
of the load transferred to end bearing depends on the relative stiffness of
the rock to concrete and the shaft geometry. Generally, the proportion
transferred to end bearing decreases for increasing depth of embedment and
for increasing rock stiffness. This proportion increases with increased
loading. Field tests indicate that the ultimate shaft resistance is
developed with very little deformation (usually less than 0.25 inches) and
that the peak resistance developed tends to remain constant with further
movement. Based on load test data, the ultimate shaft resistance can be
estimated approximately from:

= (2.3 to 3)(fw')

1/2

(pier diameter >16 inches)

= (3 to 4)(fw')

1/2

(pier diameter <16 inches)

where: S

= ultimate shaft resistance in force per shaft contact area

fw' = unconfined compressive strength of either the rock or the
concrete, whichever is weakest.

See Reference 29, Shaft Resistance of Rock Socketed Drilled Piers, by
Horvath and Kenney.

4. SETTLEMENT OF DEEP FOUNDATIONS IN ROCK. Settlement is normally
negligible and need not be evaluated for foundations on rock designed for an
appropriate allowable bearing pressure.

For very heavy or for extremely settlement sensitive structures, the
settlement can be computed based on the solution for elastic settlement
presented in Chapter 5 of DM-7.1. The choice of the elastic modulus, E, to
use in the analysis should be based on the rock mass modulus which
requires field investigation. For guidance see Reference 9 and Reference
30, Rock Mechanics in Engineering Practice, by Stagg and Zienkiewicz, eds.
In cases where the seismic Young's modulus is known, the static modulus can
be conservatively assumed to be 1/10th the seismic modulus.

Section 7. LATERAL LOAD CAPACITY

1. DESIGN CONCEPTS. A pile loaded by lateral thrust and/or moment at its
top, resists the load by deflecting to mobilize the reaction of the
surrounding soil. The magnitude and distribution of the resisting pressures
are a function of the relative stiffness of pile and soil.

Design criteria is based on maximum combined stress in the piling,
allowable deflection at the top or permissible bearing on the surrounding
soil. Although 1/4-inch at the pile top is often used as a limit, the
allowable lateral deflection should be based on the specific requirements of
the structure.

7.2-234

2. DEFORMATION ANALYSIS - SINGLE PILE.

a. General. Methods are available (e.g., Reference 9 and Reference 31,
Non-Dimensional Solutions for Laterally Loaded Piles, with Soil Modulus
Assumed Proportional to Depth, by Reese and Matlock) for computing lateral
pile load-deformation based on complex soil conditions and/or non-linear
soil stress-strain relationships. The COM 622 computer program (Reference
32, Laterally Loaded Piles: Program Documentation, by Reese) has been
documented and is widely used. Use of these methods should only be
considered when the soil stress-strain properties are well understood.

Pile deformation and stress can be approximated through application
of several simplified procedures based on idealized assumptions. The two
basic approaches presented below depend on utilizing the concept of
coefficient of lateral subgrade reaction. It is assumed that the lateral
load does not exceed about 1/3 of the ultimate lateral load capacity.

b. Granular Soil and Normally to Slightly Overconsolidated Cohesive
Soils. Pile deformation can be estimated assuming that the coefficient of
subgrade reaction, K

, increases linearly with depth in accordance with:

fz
K

))

where: K

= coefficient of lateral subgrade reaction (tons/ft

)

f = coefficient of variation of lateral subgrade reaction
(tons/ft

)

z = depth (feet)
D = width/diameter of loaded area (feet)

Guidance for selection of f is given in Figure 9 for fine-grained
and coarse-grained soils.

c. Heavily Overconsolidated Cohesive Soils. For heavily
overconsolidated hard cohesive soils, the coefficient of lateral subgrade
reaction can be assumed to be constant with depth. The methods presented in
Chapter 4 can be used for the analysis; K

varies between 35c and 70c

(units of force/length

where c is the undrained shear strength.

d. Loading Conditions. Three principal loading conditions are
illustrated with the design procedures in Figure 10, using the influence
diagrams of Figure 11, 12 and 13 (all from Reference 31). Loading may be
limited by allowable deflection of pile top or by pile stresses.

Case I. Pile with flexible cap or hinged end condition. Thrust and
moment are applied at the top, which is free to rotate. Obtain total
deflections moment, and shear in the pile by algebraic sum of the effects of
thrust and moment, given in Figure 11.

7.2-235

7.2.236

7.2-237

7.2-238

7.2-239

7.2-240

Case II. Pile with rigid cap fixed against rotation at ground
surface. Thrust is applied at the top, which must maintain a vertical
tangent. Obtain deflection and moment from influence values of Figure 12.

Case III. Pile with rigid cap above ground surface. Rotation of
pile top depends on combined effect of superstructure and resistance below
ground. Express rotation as a function of the influence values of Figure 13
and determine moment at pile top. Knowing thrust and moment applied at pile
top, obtain total deflection, moment and shear in the pile by algebraic sum
of the separate effects from Figure 11.

3. CYCLIC LOADS.

Lateral subgrade coefficient values decrease to about 25% the initial value
due to cyclic loading for soft/loose soils and to about 50% the initial
value for stiff/dense soils.

4. LONG-TERM LOADING. Long-term loading will increase pile deflection
corresponding to a decrease in lateral subgrade reaction. To approximate
this condition reduce the subgrade reaction values to 25% to 50% of their
initial value for stiff clays, to 20% to 30% for soft clays, and to 80% to
90% for sands.

5. ULTIMATE LOAD CAPACITY - SINGLE PILES. A laterally loaded pile can fail
by exceeding the strength of the surrounding soil or by exceeding the
bending moment capacity of the pile resulting in a structural failure.
Several methods are available for estimating the ultimate load capacity.

The method presented in Reference 33, Lateral Resistance of Piles in
Cohesive Soils, by Broms, provides a simple procedure for estimating
ultimate lateral capacity of piles.

6. GROUP ACTION. Group action should be considered when the pile spacing
in the direction of loading is less than 6 to 8 pile diameters. Group
action can be evaluated by reducing the effective coefficient of lateral
subgrade reaction in the direction of loading by a reduction factor R
(Reference 9) as follows:

Pile Spacing in Subgrade Reaction
Direction of Loading Reduction Factor
D = Pile Diameter R

)))))))))))))))))))))

)))))))))))))))))

8D 1.00
6D 0.70
4D 0.40
3D 0.25

7.2-241

REFERENCES

1. Teng, W.C., Foundation Design, Prentice Hall International, 1962

2. Skempton, A.W., The Bearing Capacity of Clays, Proceedings, Building
Research Congress, London, 1951.

3. Tomlinson, M.F., The Adhesion of Piles Driven in Clay Soils,
Proceedings, Fourth International Conference on Soil Mechanics and
Foundation Engineering, London, 1957.

4. Departments of the Army and Air Force, Soils and Geology, Procedures
for Foundation Design of Buildings and Other Structures (Except
Hydraulic Structures), TM5/818-1/AFM88-3, Chapter 7, Washington, D.C.
1979.

5. Meyerhof, G.G., and Hanna, A.M., Ultimate Bearing Capacity of
Foundations on Layered Soils Under Inclined Load Canadian Geotechnical
Journal, Vol. 15, No. 4, 1978.

6. Vesic, A.S., Design of Pile Foundations, National Cooperative Highway
Research Program Synthesis 42, Transportation Research Board, 1977.

7. Meyerhof, G.G., Bearing Capacity and Settlement of Pile Foundations,
Journal of Geotechnical Engineering Division, ASCE, Vol. 102, No. GT3,
1976.

8. Baguelin, F., Jexequel, J.F., and Shields, D.H., The Pressuremeter and
Foundation Engineering, TransTech Publications, 1978.

9. Canadian Geotechnical Society, Canadian Foundation Engineering Manual,
Canadian Geotechnical Society, 1978.

10. Smith, E.A., Pile Driving by the Wave Equation, Transactions, American
Society of Civil Engineers, Vol. 127, Part II, pp 1145-193, 1962.

11. Rausche, F., Moses, F., and Goble, G.G., Soil Resistance Predictions
from Pile Dynamics, Journal of the Soil Mechanics and Foundation
Division, ASCE, Vol. 98, No. SM9, 1972.

12. Meyerhof, G.G., Ultimate Bearing Capacity of Footings on Sand Layer
Overlying Clay, Canadian Geotechnical Journal, Vol. 11, No. 2, 1974.

13. Whitaker, T., Experiments with Model Piles in Groups, Geotechnique,
London, 1957.

14. Tomlinson, M.J., Pile Design and Construction Practice, Viewpoint
Publications, Cement and Concrete Association, London, 1957.

15. Garlanger, J.E., Prediction of the Downdrag Load at Culter Circle
Bridge, Symposium on Downdrag of Piles, Massachusetts Institute of
Technology, 1973.

16. Fellenius, B.H., Downdrag on Piles Due to Negative Skin Friction,
Canadian Geotechnical Journal, Vol. 9, No. 4, 1972.

7.2-242

17. Claessen, A.I.M. and Horvat, E., Reducing Negative Skin Friction with
Bitumen Slip Layers, Journal of the Geotechnical Engineering Division,
ASCE, Vol. 100, No. GT8, 1974.

18. Bjerrum, L., Johannessin, I.J., and Eide, O., Reduction of Negative
Skin Friction on Steel Piles to Rock, Proceedings of the Seventh
International Conference on Soil Mechanics and Foundation Engineering,
Vol. 2, pp 27-34, 1960.

19. Deep Foundation Institute, Inspectors' Manual for Deep Foundations, The
Deep Foundations Institute, Springfield, NJ, 1978.

20. AWPI, Technical Guidelines for Pressure-Treated Wood, Timber Piling, P1
American Wood Preservers Institute, 1976.

21. ACI Committee 543, Recommendations for Design, Manufacture and
Installation of Concrete Piles, ACI Manual of Concrete Practice,
American Concrete Institute, Part 3, October, 1974.

22. Reese, L.C. and Wright,S.J., Drilled Shafts: Design and Construction,
Guideline Manual, Vol. 1; Construction Procedures and Design for Axial
Load, Federal Highway Authority, July, 1977.

23. Garneau, R., and Samson, L., A Device for the Constant Rate of
Penetration Test for Piles, Canadian Geotechnical Journal, Vol. 11, No.
2, 1974.

24. Davisson, M.T. and Salley, J.R., Model Study of Laterally Loaded Pile,
Journal of Soil Mechanics and Foundation Division, ASCE, Vol. 96, No.
SM5, 1970.

25. Chellis, R.D., Pile Foundations, McGraw Hill Book Company, 1961

26. Abbett, American Civil Engineering Practice, Vol. 1.

27. Johnson, S.M. and Kavanaugh, T.C., The Design of Foundations for
Buildings, McGraw Hill Book Company, 1968.

28. Peck, R.B., Hanson, W.E., and Thornburn, T.H., Foundation Engineering,
John Wiley & Sons, Inc., 1974.

29. Horvath, N.G. and Kenney, T.C., Shaft Resistance of Rock-Socketed
Drilled Pier, ASCE, Preprint #3698, 1979.

30. Stagg, K.G. and Zienkiewiez, O.C., Eds., Rock Mechanics in Engineering
Practice, John Wiley & Sons, Inc., 1968.

31. Reese, L.C. and Matlock, H., Non-Dimensional Solutions for Laterally
Loaded Piles with Soil Modulus Assumed Proportional to Depth,
Proceedings, Eighth Texas Conference on Soil Mechanics and Foundation
Engineering, Austin, Texas, ASCE, 1956.

7.2-243 Change 1, September 1986

32. Reese, L.C., Laterally Loaded Piles: Program Documentation, Journal
of Geotechnical Engineering Division, ASCE, Vol. 103, No. GT4, 1977.

33. Broms, B.B., Lateral Resistance of Piles in Cohesive Soils, Journal of
Soil Mechanics and Foundations Division, ASCE, Vol. 90, No. SM2 and
SM3, 1964.

34. Naval Facilities Engineering Command

Design Manuals (DM)
DM-25.06 General Criteria for Waterfront Construction
DM-38.04 Pile Driving Equipment

Copies of Guide Specifications and Design Manuals may be obtained from
the U.S. Naval Publications and Forms Center, 5801 Tabor Avenue,
Philadelphia, PA 19120.

Change 1, September 1986 7.2-244

BIBLIOGRAPHY

American Petroleum Institute, Recommended Practice for Planning,
Designing and Constructing Fixed Offshore Platforms, API RP 2A, January
1971.

Casagrande, L., Comments on Conventional Design of Retaining Wall
Structures, Journal of the Soil Mechanics and Foundation Engineering
Division, ASCE, Vol. 99, No. SM2, 1973.

Davisson, M.T., Inspection of Pile Driving Operations, Tech. Report M-22,
Cold Regions Research Engineering Laboratories Corps of Engineers, U.S.
Department of the Army, 1972.

Foster, C.R., Field Problems: Compaction, Foundation Engineering,
Leonards, G.A., Editor, McGraw-Hill Book Co., Inc., New York, Chapter
12, 1952.

Fuller, F.N. and Hoy, H.E., Pile Load Tests Including Quick Load Test
Method, Conventional Methods and Interpretations, Highway Research Record
No. 333, HRB U.S. National Research Council, pp 74-86, 1970.

Hunt, H.W., Design and Installation of Pile Foundations, Associated Pile
Fitting Corporation, Clifton, NJ, 1974.

McClelland, B., Design of Deep Penetration Piles for Ocean Structures,
Terzaghi Lectures: 1963-1 72, ASCE, New York, pp 383-421, 1974.

Meyerhof, G.G., Bearing Capacity and Settlement of Pile Foundations,
Journal of the Geotechnical Engineering Division, ASCE, Vol. 102, No.
GT3, 1976.

National Bureau of Standards, Corrosion of Steel Pilings in Soils,
Monographs 58 and 127, U.S. Department of Commerce, Washington, D.C.

Reese, L.C. and Welch, R.C., Lateral Loading of Deep Foundations in Stiff
Clay, Journal of the Geotechnical Engineering Division, ASCE, Vol. 101,
No. GT7, 1975.

USBR, Earth Manual, Second Edition, U.S. Department of Interior, Bureau
of Reclamation, U.S. Government Printing Office, Washington, D.C., 1974.

Vesic, A.S., Ultimate Loads and Settlements of Deep Foundations in Sand,
Procs., Symposium on Bearing Capacity and Settlement of Foundations, Duke
University, Durham, NC., 1967.

Winterkorn, H.F., and Fang, H.Y., Editors, Foundation Engineering
Handbook, Van Nostrand Reinhold Co., New York, 1975.

Woodward, R.J., Gardner, W.S. and Greer, D.M., Drilled Pier Foundations,
McGraw-Hill Book Co., Inc., New York, 1972.

7.2-B-1

APPENDIX A
Listing of Computer Programs

+))))))))))))))))0))))))))))))))0)))))))))))))))))))))0))))))))))))))))))))))))))),

Subject

Program

Description

Availability

/))))))))))))))))3))))))))))))))3)))))))))))))))))))))3)))))))))))))))))))))))))))1

Shallow

QULT GESA

Bearing capacity

Geotechnical Engineering

Foundations

Catalog No.

analysis by Balla,

Software Activity

(Chapter 4)

E03-0001-

Brinch Hansen,

University of Colorado

00043

Meyerhof-Prandtl,

Boulder, CO 80309

Sokoluvski and

Terzaghi Methods

/))))))))))))))))3))))))))))))))3)))))))))))))))))))))3)))))))))))))))))))))))))))1

Excavation, and

SOIL-STRUCT

Two dimensional

Stanford University

Earth Pressures

finite element

(Chapter 1) and

program to

(Chapter 3)

analyze tieback

walls.

SSTINCS-2DFE

Two dimensional

Virginia Polytechnic

finite element

Institute and State

program to analyze

University, Blacksburg,

tieback walls.

VA 24061

/))))))))))))))))3))))))))))))))3)))))))))))))))))))))3)))))))))))))))))))))))))))1

Deep Foundations

COM622 GESA

Program solves for

GESA or University of

(Chapter 5)

Catalog No.

deflection and

Austin

E04-0003-

bending moment in

00044

a laterally loaded

pile based on

theory of a beam

on an elastic

foundation using

finite difference

techniques. Soil

properties are

defined by a set

of load-deflection

curves.

TTI

Program for

U.S. Department of

analysis of pile

Transportation FHWA R & D

driving by the

Implementation Div.

Wave Equation;

developed at Texas

A & M University.

WEAP GESA

Wave Equation

GESA

Catalog No.

analysis for pile

E04-0004-

driven by impact

00046

hammers, diesel

hammers and

air/steam hammers.

.))))))))))))))))2))))))))))))))2)))))))))))))))))))))2)))))))))))))))))))))))))))-

7.2-A-1

APPENDIX A
Listing of Computer Programs (continued)

+))))))))))))))))0))))))))))))))))))0)))))))))))))))))))))0))))))))))))))))))))))),

Subject

Program

Description

Availability

/))))))))))))))))3))))))))))))))))))3)))))))))))))))))))))3)))))))))))))))))))))))1

Deep Foundations

WINIT

Auxiliary program

GESA

(Chapter 5)

GESA Catalog No.

for WEAP.

EO4-005-00047

WEHAM

Hammer data for

GESA Catalog No.

WEAP.

E04-006-00048

WDATA

WEAP data

GESA Catalog No.

generator.

E04-007-00049

.))))))))))))))))2))))))))))))))))))2)))))))))))))))))))))2)))))))))))))))))))))))-

7.2-A-2

GLOSSARY

Downdrag. Force induced on deep foundation resulting from downward movement
of adjacent soil relative to foundation element. Also referred to as
negative skin friction.

Homogenous Earth Dam. An earth dam whose embankment is formed of one soil
type without a systematic zoning of fill materials.

Modulus of Subgrade Reaction. The ratio between the bearing pressure of a
foundation and the corresponding settlement at a given point.

Nominal Bearing Pressures. Allowable bearing pressures for spread
foundation on various soil types, derived from experience and general usage,
which provide safety against shear failure or excessive settlement.

Optimum Moisture Content. The moisture content, determined from a
laboratory compaction test, at which the maximum dry density of a soil is
obtained using a specific effort of compaction.

Piping. The movement of soil particles as the result of unbalanced seepage
forces produced by percolating water, leading to the development of boils or
erosion channels.

Swell. Increase in soil volume, typically referring to volumetric expansion
of particular soils due to changes in water content.

Zoned Earth Dam. An earth dam embankment zoned by the systematic
distribution of soil types according to their strength and permeability
characteristics, usually with a central impervious core and shells of
coarser materials.

7.2-G-1

SYMBOLS

Symbol Designation

A Cross-sectional area.
A

Anchor pull in tieback system for flexible wall.

B,b Width in general, or narrow dimension of a foundation unit.
c

Unit adhesion between soil and pile surface or surface of some

other foundation material.
C

all

Allowable cohesion that can be mobilized to resist shear

stresses.
C

Shape factor coefficient for computation of immediate

settlement.
c Cohesion intercept for Mohr's envelope of shear strength based
on total stresses.
c' Cohesion intercept for Mohr's envelope of shear strength based
on effective stresses.
c

Coefficient of consolidation.

D,d Depth, diameter, or distance.
D

Relative density.

, D

Grain Size division of a Soil sample, percent of dry weight

smaller than this grain size is indicated by subscript.

E Modulus of elasticity of structural Material.
E

Modulus of elasticity or "modulus of deformation" of soil.

e Void ratio.
F

Safety factor in stability or shear strength analysis.

f Coefficient of variation of soil modulus of elasticity with
depth for analysis of laterally loaded piles.
G Specific gravity of solid particles in soil sample, or shear
modulus of soil.
H,h In general, height or thickness.
H

Height of groundwater or of open water above a base level.

I Influence value for vertical stress produced by superimposed
load, equals ratio of stresses at a point in the foundation
to intensity of applied load.
i Gradient of groundwater pressures in underseepage analysis.
K

Coefficient of active earth pressures.

Ratio of horizontal to vertical earth pressures on side of pile

or other foundation.
k

Coefficient of lateral subgrade reaction.

Coefficient of passive earth pressures.

Modulus of subgrade reaction for bearing plate or foundation of

width b.
K

Modulus of subgrade reaction for 1 ft square bearing plate at

ground surface.
k Coefficient of permeability.
ksf Kips per sq ft pressure intensity.
ksi Kips per sq in pressure intensity.

7.2-S-1

Symbol Designation

L,1 Length in general or longest dimension of foundation unit.
N

, N

, Bearing capacity factors.

, N[gamma],

N [gamma]q
N

Stability number for slope stability.

n Porosity of soil sample.
n

Effective porosity.

OMC Optimum moisture content of compacted soil.
P

Resultant active earth force.

Component of resultant active force in horizontal direction.

pcf Density in pounds per cubic foot.
P

Resultant horizontal earth force.

Resultant passive earth force.

Component of resultant passive earth force in horizontal

direction.
P

Resultant vertical earth force.

Resultant force of water pressure.

p Intensity of applied load.
P

Existing effective overburden pressure acting at a specific

height in the soil profile.
P

Preconsolidation pressure.

all

Allowable load capacity of deep foundation element.

ult

Ultimate load that causes shear failure of foundation unit.

q Intensity of vertical load applied to foundation unit.
q

all

Allowable bearing capacity of shallow foundation unit.

Unconfined compressive strength of soil sample.

ult

Ultimate bearing pressure that causes shear failure of

foundation unit.
R,r Radius of well or other right circular cylinder.
s Shear strength of soil for a specific stress or condition in
situ, used instead of strength parameters c and [theta].
T Thickness of soil stratum, or relative stiffness factor of
soil and pile in analysis of laterally loaded piles.
Z Depth.
[gamma]

Dry unit weight of soil.

[gamma]

Effective unit weight of soil.

[gamma]

MAX

Maximum dry unit weight of soil determined from moisture

content dry unit weight curve; or, for cohesionless soil,
by vibratory compaction.
[gamma]

MIN

Minimum dry unit weight.

[gamma]

SUB

Submerged (buoyant) unit weight of soil mass.

[gamma]

Wet unit weight of soil above the groundwater table.

[gamma]

Unit weight of water, varying from 62.4 pcf for fresh

water to 64 pcf for sea water.
[RHO] Magnitude of settlement for various conditions.
[phi] Angle of internal friction or "angle of shearing
resistance," obtained from Mohr's failure envelope for
shear strength.
[Upsilon] Poisson's Ratio.

7.2-S-2

INDEX

Anchorages, tower guy...........7.2-169
See Foundations, shallow,
Tower Guy Anchorages

Bibliography....................7.2-B-1

Cofferdams, double-wall.........7.2-116
See Walls and retaining
structures.
Compaction procedures...........7.2-45
Computer Programs, Listing of...7.2-A-1

Embankments compacted, compaction
compaction procedures, and
hydraulic fills...............7.2-37
Applications.................7.2-37
Compaction control,
embankment.................7.2-50
Analysis of control
test data...............7.2-51
Compactive effort......7.2-52
Moisture control.......7.2-52
Statistical study......7.2-52
Number of field density
tests...................7.2-51
Number of laboratory
compaction tests........7.2-51
Compaction requirements
and procedures.............7.2-45
Material type influence...7.2-45
Oversize effect........7.2-45
Soils insensitive to
compaction moisture..7.2-45
Soils sensitive to
compaction moisture..7.2-45
Methods...................7.2-45
Requirements..............7.2-45
Specification
provisions...........7.2-45
Cross-section design.........7.2-38
Earth dam embankments.....7.2-41
Piping and cracking....7.2-41
Seepage control........7.2-41

Embankment compacted, compaction
procedures, and hydraulic fills
(continued)
Cross-section design (continued)
Material type influence....7.2-38
Utilization.............7.2-38
Settlement.................7.2-38
Embankment
consolidation.........7.2-38

Foundation settlement...7.2-38
Secondary compression...7.2-41
Stable foundation..........7.2-38
Weak foundation............7.2-38
Excavation, borrow............7.2-52
Methods of excavation......7.2-53
Utilization of excavated
materials................7.2-53
Borrow volume...........7.2-53
Rock fill...............7.2-53
Fills, hydraulic and
underwater................ 7.2-54
Construction methods.......7.2-54
Hydraulic fill on
land..................7.2-54
Underwater fills........7.2-54
Performance of fill
materials................7.2-54
Coarse-grained fills....7.2-54
Hard clay fills.........7.2-56
Equipment, pile driving.........7.2-213
See Foundations, deep,
Types.
Excavation, borrow..............7.2-52
See Embankments, compacted,
Excavation.

Fills, hydraulic and
underwater....................7.2-54
See Embankments compacted,
Fills.

Foundations, deep...............7.2-177
Application..................7.2-177
Bearing capacity.............7.2-191
Dynamic Driving
Resistance..............7.2-202
Pile group, theoretical...7.2-204
Single pile, theoretical..7.2-192

7.2-INDEX-1

Foundations, deep (continued)
Distribution of loads on
pile groups................7.2-230
Downdrag.....................7.2-209
Installation.................7.2-213
Investigation program........7.2-177
Lateral load capacity........7.2-234
Load tests...................7.2-228
Rock, deep foundations on....7.2-232
Settlement...................7.2-207
Pile group................7.2-209
Single pile...............7.2-207
Types........................7.2-178
Allowable stresses........7.2-179
Design criteria...........7.2-179
Foundations, shallow............7.2-129
Applications.................7.2-129
Bearing capacity.............7.2-129
Footings, proportioning
individual..............7.2-146
Nominal bearing pressures.7.2-141
Modifications.............7.2-141
Utilization...............7.2-141
Ultimate shear failure.......7.2-129
Bearing capacity diagrams.7.2-129
Theoretical bearing
capacity................7.2-129
Uplift capacity..............7.2-169
Rock anchorages...........7.2-169
Soil anchorages...........7.2-169
Collapsing soils.............7.2-163
Engineered fill..............7.2-159
Compaction control........7.2-159
Utilization...............7.2-159
Expansive soils..............7.2-159
Eliminating swell.........7.2-161
Minimizing swell effects..7.2-161
Potential swelling
conditions..............7.2-159
Mat and continuous beam
foundations................7.2-150
Applications..............7.2-150
Design....................7.2-150
Settlement................7.2-150
Stability requirements....7.2-150
Tower guy anchorages.........7.2-169
Anchoring tower guy
loads...................7.2-169
Deadman anchorages.....7.2-172
Piling anchorages......7.2-233
Rock...................7.2-169

Foundations, shallow (continued)
Underdraining and
waterproofing..............7.2-163
Pressure slabs............7.2-163
Relieved slabs............7.2-169
Waterproofing
requirements............7.2-169

Glossary........................7.2-G-1

Mat foundations.................7.2-150
See Foundations, shallow,
Mat.

Piles:
Foundations (see Foundations,
deep)......................7.2-177

Symbols.........................7.2-S-1

Walls and retaining structures,
analysis......................7.2-59
Cofferdams, double-wall......7.2-116
Analysis..................7.2-116
Exterior pressures.....7.2-116
Stability
requirements.........7.2-116
Cell fill.................7.2-125
Drainage...............7.2-125
Materials..............7.2-125
Types.....................7.2-116
Flexible walls design........7.2-85
Anchored bulkheads........7.2-85
Anchorage system.......7.2-90
Computation example....7.2-93
Construction
precautions..........7.2-90
Drainage...............7.2-85
Movements, wall........7.2-85
Pressures, wall........7.2-85
Braced sheet pile walls...7.2-90
Computation example....7.2-107
Narrow cuts braced.....7.2-101

7.2-INDEX-2

Walls and retaining structures,
analysis (continued)
Flexible walls design (continued)
Braced sheet pile walls
continued)
Raking braces with
wall..............7.2-101
Stability of base of
excavation........7.2-104
Tied backwalls......7.2-101
Crib walls................7.2-116
Gabions...................7.2-112
Pressures, wall,
computations...............7.2-59
Active pressures..........7.2-59
Stratified backfill,
sloping groundwater
level................7.2-61
Uniform backfill, no
groundwater..........7.2-61
Uniform backfill,
static groundwater...7.2-61
Coefficients with wall
friction................7.2-61
Effect of construction
procedures..............7.2-76
Compacted fills........7.2-76
Hydraulic fills........7.2-76
Effect of seepage and
Drainage................7.2-70
Beneath walls seepage..7.2-70
Conditions, general....7.2-70
Rainfall on drained
walls................7.2-70
Static differential
head................7.2-70
Loading, surcharge........7.2-70
Area loads.............7.2-73
Live loads.............7.2-73
Movement, wall............7.2-73
Braced flexible
sheeting.............7.2-73
Restrained walls.......7.2-76
Tilting retaining
walls................7.2-73
Passive pressures.........7.2-59
Stratified backfill,
sloping groundwater
level................7.2-61
Uniform backfill, no
groundwater..........7.2-61
Uniform backfill,
static groundwater
level................7.2-61

Walls and retaining structures,
analysis (continued)
Pressures, wall, computation
(continued)
Reinforced earth..........7.2-116
Rigid retaining walls.....7.2-82

Criteria, general......7.2-82
Drainage...............7.2-85
Settlement and
overturning..........7.2-82
Stability..............7.2-82
High walls................7.2-82
Low walls.................7.2-85
Drainage...............7.2-85
Equivalent fluid
pressures............7.2-85

7.2-INDEX-3

*U.S. GOVERNMENT PRINTING OFFICE : 1988 0 - 198-094

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